Topic 12 · Chemical reactions and conservation of mass — the scripts

What you are deciding: go-ahead for video generation on this topic, card by card.

Out of scope: articles and PP100 items (not on this page).

Here: the intro video, 8 lesson videos (4 marked by the author as “could do without a video”) and the summary video, in teaching order. Each card: the script, the attached question, then the quiz the student meets after the video.

How: tap one button per card. Taps and notes save as you go and are sent; the Notes tab shows what has gone and re-sends.

Intro video · teaches nothing, opens the question117 words · about 0:58

Introduction: Chemical reactions and conservation of mass

Script
SayScreen
Here is a pad of steel wool on a balance, and the balance reads 10.0 grams.[the shiny pad on the balance; readout 10.0 g]
After a week damp in the air, the pad turns brown and crumbly.[the pad browns]
Back on the balance it reads 11.2 grams, and nobody added anything.[readout 11.2 g]
And here is a tree that grew from 2.3 kilograms to 76.7 kilograms while its soil barely changed.[a small tree, then a tall one, the soil line the same]
So where does the extra mass come from, and can mass ever go missing?[the pad and the tree side by side; question mark]
To find out, we will look at what happens to the atoms when one substance turns into another, and what happens to the mass.[the two scenes stay]
Okay, so are you ready to find out where a rusting pad's extra mass comes from?[the three replies appear]

The ready line's poll — the attached item (no key; the intro teaches nothing)

video

Okay, so are you ready to find out where a rusting pad's extra mass comes from?

  1. A Yes, let's go! — Great. Here we go.
  2. B Not sure yet — That's fine. We take it one step at a time.
  3. C Let me watch that again — Good idea. Watch it again, then come back.
Answer

No key. A poll: every reply is accepted with its friendly line.

Your note · the intro video
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 1 of 8Author: definitely a video200 words · about 1:40

Where the new substance's atoms come from

MAT-068 · Atoms are rearranged in a reaction, not created or destroyed — Explain where the atoms in the products of a reaction come from.

Script
SayScreen
Suppose you leave a pad of steel wool damp in the air for a week.[a shiny pad on a balance; readout 10.0 g]
On day one the balance read 10.0 grams; a week later the pad is brown and crumbly, and it reads 11.2 grams.[the pad browns; readout 11.2 g]
Nobody added anything: where did the extra 1.2 grams come from?[question mark over the readout]
The extra 1.2 grams came from the air.[the air above the pad highlighted]
The shiny pad is iron atoms, and the air holds pairs of oxygen atoms.[before box: gray circles; pairs of large open circles drift above; key chip: gray circle = iron atom, large open circle = oxygen atom]
Watch the oxygen atoms land on the iron atoms and join on.[a large open circle slides onto each gray circle and touches it]
Iron atoms joined to oxygen atoms make a new substance, iron oxide: rust.[after box: gray–open pairs; label: iron oxide (rust)]
As each oxygen atom joins, the reading climbs.[the readout counts up beside the box: 10.4, 10.8, 11.2 g]
Chemists write the change on one line: iron and oxygen react to make iron oxide.[strip: iron + oxygen → iron oxide]
Now consider a copper pan heated over a flame.[a copper pan over a flame]
A black coat grows, and the pan gains mass.[a black coat spreads; readout climbs]
Oxygen atoms from the air joined the copper atoms.[strip: copper + oxygen → copper oxide]
So, here's what we've seen. The atoms in a new substance come from the substances that were there before.[the rule slide: the rust before-and-after boxes with counts 4 and 4; chip ATOMS; nothing else printed]
No atom is made from nothing, and no atom is lost.[the counts 4 and 4 glow under both boxes]
So the pad's extra 1.2 grams is the mass of the oxygen atoms that joined on.[the pad on the balance; 11.2 g]
Okay, now your turn.[closing screen: bullets — • The atoms in a new substance come from the substances that were there before • No atom is made from nothing, and no atom is lost]

“Okay, now your turn.” — the attached question

video

Steel wool rusts in damp air, and its balance reading climbs from 10.0 g to 11.2 g. What is the extra mass?

  1. A iron atoms that grew bigger
  2. B oxygen atoms that joined on
  3. C water soaked into the pad
Answer

Key: B — oxygen atoms that joined on

Oxygen atoms from the air join onto the iron atoms.
Each oxygen atom has its own mass.
So the extra 1.2 g is the mass of the oxygen atoms that joined on.

Feedback per option

  • A An atom does not grow; oxygen atoms from the air land on the iron and join on.
  • B Oxygen atoms from the air land on the iron atoms and join on, and the reading climbs with each one.
  • C Nothing soaks in; oxygen atoms join the iron atoms.

Quiz after the video — the mastery check, 10 items

Q1recall

In a chemical change, what forms?

  1. A a new substance
  2. B the same substance in a new shape
  3. C the same substance in a new state
Answer

Key: A — a new substance

A chemical change is a change in which a new substance forms.
The new substance has its own properties.
So in a chemical change, a new substance forms.

Feedback per option

  • A A chemical change is a change in which a new substance forms.
  • B A new shape of the same substance is a physical change, not a chemical change.
  • C A new state of the same substance is a physical change, not a chemical change.
Q2recall

What is the smallest piece of iron that is still iron?

  1. A one grain of iron
  2. B one atom of iron
  3. C a piece smaller than an atom
Answer

Key: B — one atom of iron

Every material is made of atoms.
One atom of iron is the smallest piece that is still iron.
Anything smaller is not iron.

Feedback per option

  • A A grain of iron holds many, many iron atoms; each atom is a smaller piece that is still iron.
  • B Every material is made of atoms, and one atom of iron is the smallest piece that is still iron.
  • C A piece smaller than one atom is not iron anymore.
Q3what

Suppose a 20.0 g iron chain is left damp for a month and turns brown and crumbly. The chain, rust and all, goes back on the balance. What does the balance read?

  1. A less than 20.0 g
  2. B exactly 20.0 g
  3. C more than 20.0 g
Answer

Key: C — more than 20.0 g

The rust is iron atoms joined to oxygen atoms.
The oxygen atoms came from the air and joined on.
Each oxygen atom has its own mass, so the balance reads more than 20.0 g.

Feedback per option

  • A No iron atom left the chain; oxygen atoms from the air joined on, so the mass went up, not down.
  • B Oxygen atoms from the air joined onto the iron atoms, and each has its own mass, so the reading went up.
  • C Oxygen atoms from the air joined onto the iron atoms, and each oxygen atom has its own mass.
Q4why

Suppose a shiny zinc strip is heated in air. A white powder forms on it, and the strip with its powder has more mass than the shiny strip. Explain where the extra mass came from.

Starter: The atoms in a new substance come from…

Answer

Model answer · ['the atoms in the new substance came from the substances that were there before', 'oxygen atoms from the air joined onto the zinc atoms', 'each oxygen atom has its own mass, so the extra mass is the oxygen atoms that joined on'] points

The atoms in a new substance come from the substances that were there before.
The zinc atoms joined with oxygen atoms from the air.
The white powder is zinc atoms joined to oxygen atoms.
Each oxygen atom has its own mass.
So the extra mass is the mass of the oxygen atoms that joined on.
Q5what

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. How many large open circles does the after box hold?

beforeafter

Typed answer

Answer

Accepted: 4 · four · 4 circles · 4 large open circles

Count the large open circles in the before box: two pairs, 4 circles.
Every atom that was there before is still there after.
Count the after box: 4 large open circles, now joined to gray circles.
Q6what

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Where did the small dark circles in the after box come from?

beforeafter
  1. A the change made them
  2. B from outside the boxes, in the air
  3. C from the before box
Answer

Key: C — from the before box

Count the small dark circles in the before box: two pairs, 4 atoms.
The atoms in the new particles come from the particles that were there before.
So the 4 small dark circles in the after box were in the before box already.

Feedback per option

  • A No atom is made from nothing; count the small dark circles in the before box and you find the same four.
  • B Nothing came in from outside the boxes; the before box already holds four small dark circles.
  • C The before box holds two pairs of small dark circles, four atoms; the after box holds the same four, joined to new partners.
Q7fluency

Iron oxide forms on a damp iron railing. Where did the oxygen atoms in the iron oxide come from?

  1. A from the iron itself
  2. B from the air around the railing
  3. C from nowhere at all
Answer

Key: B — from the air around the railing

The air around the railing holds oxygen.
Oxygen atoms from the air joined onto the iron atoms.
So the air supplied the oxygen atoms in the iron oxide.

Feedback per option

  • A Iron atoms stay iron atoms; they cannot turn into oxygen atoms.
  • B The air holds oxygen, and its oxygen atoms joined onto the iron atoms.
  • C No atom is made from nothing; the oxygen atoms were in the air already.
Q8misconception

Cormac says: "When steel wool rusts, the change makes new oxygen atoms inside the rust." Is Cormac correct?

  1. A yes
  2. B no
Answer

Key: B — no

The atoms in a new substance come from the substances that were there before.
The oxygen atoms in the rust were in the air before the change.
The change joined them onto the iron atoms, so Cormac is not correct.

Feedback per option

  • A Cormac's claim needs atoms made from nothing. No atom is made from nothing: the oxygen atoms were in the air already, and the change joined them onto the iron.
  • B The oxygen atoms were in the air before the change; the change only joined them onto the iron atoms.
Q9transfer

A copper roof turns green over many years. The green layer is a new substance: copper atoms joined to other kinds of atom. Where did those other atoms come from?

  1. A from the air around the roof
  2. B from nowhere at all
  3. C from the copper atoms, which turned into them
Answer

Key: A — from the air around the roof

The atoms in a new substance come from the substances that were there before.
The roof touched only the air.
So the other atoms in the green layer came from the air.

Feedback per option

  • A The atoms in a new substance come from the substances that were there before: here, the air around the roof.
  • B No atom is made from nothing; the other atoms were in the air already.
  • C A copper atom stays a copper atom; the other atoms came from the air.
Q10transfer

A magnesium ribbon burns in air with a bright white flame and leaves a white ash. The ash has more mass than the ribbon. What is the extra mass?

  1. A heat from the flame that soaked into the ribbon
  2. B oxygen atoms that joined onto the magnesium
  3. C magnesium atoms that grew bigger in the flame
Answer

Key: B — oxygen atoms that joined onto the magnesium

The white ash is magnesium atoms joined to oxygen atoms.
The oxygen atoms came from the air and joined on.
Each oxygen atom has its own mass, so the ash has more mass than the ribbon.

Feedback per option

  • A Heat is not matter and has no mass; the extra mass is atoms that joined on.
  • B Oxygen atoms from the air joined onto the magnesium atoms, and each oxygen atom has its own mass.
  • C An atom does not grow; the extra mass is oxygen atoms from the air that joined on.
Your note · lesson 1: Where the new substance's atoms come from
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 2 of 8Author: definitely a video189 words · about 1:34

A chemical reaction rearranges atoms

MAT-066 · Chemical reaction — Identify a chemical reaction by recognising that atoms are rearranged to form new substances.

Script
SayScreen
Here are three changes drawn before and after: ice melting, sugar dissolving, and hydrogen burning in oxygen.[three before-and-after pairs in a row]
Which of these three changes makes a new substance?[the three pairs; a question mark fades in over them]
Hydrogen burning does. Watch hydrogen burn: each pair of hydrogen atoms lets go, and each pair of oxygen atoms lets go.[the third pair comes forward; the pairs separate in the before box]
Now each oxygen atom joins two hydrogen atoms: a water molecule, a new substance.[the atoms regroup into four water molecules; label: water]
Count the circles: the same 8 hydrogen atoms and 4 oxygen atoms before and after.[counts appear under both boxes]
Now watch ice melt: the water molecules move, but every atom keeps its partners.[the same five molecules drift; no atom lets go; cross]
A change in which atoms rearrange into new substances is called a chemical reaction.[chip: CHEMICAL REACTION over the hydrogen pair]
Now consider charcoal burning: each carbon atom joins two oxygen atoms, a chemical reaction.[key chip: gray circle = carbon atom; carbon and oxygen pairs regroup into carbon dioxide; tick]
And when sugar dissolves, the sugar molecules spread among the water molecules, still whole, so that is not a reaction.[sugar molecules drift apart among water molecules; cross]
Each reaction goes on one line: hydrogen plus oxygen makes water.[strip: hydrogen + oxygen → water]
So, here's what we've seen. In a chemical reaction the atoms let go of their old partners and join new ones.[the rule slide: the hydrogen before-and-after pair; chip CHEMICAL REACTION; nothing else printed]
So new substances form.[label: water, on the after box]
Of the three drawings, only hydrogen burning shows atoms changing partners.[the third pair comes forward; tick]
Okay, now your turn.[closing screen: one line — "In a chemical reaction the atoms let go of their old partners and join new ones."]

“Okay, now your turn.” — the attached question

video

Ice melts, sugar dissolves, and hydrogen burns in oxygen. In which change do the atoms change partners?

  1. A ice melting
  2. B sugar dissolving
  3. C hydrogen burning
Answer

Key: C — hydrogen burning

In hydrogen burning, the hydrogen pairs and the oxygen pairs let go.
Each oxygen atom joins two hydrogen atoms, making water.
So hydrogen burning makes the atoms change partners: a chemical reaction.

Feedback per option

  • A When ice melts, every water molecule keeps its atoms; they only move.
  • B When sugar dissolves, every sugar molecule stays whole among the water molecules.
  • C When hydrogen burns, the pairs let go and each oxygen atom joins two hydrogen atoms: water.

Quiz after the video — the mastery check, 13 items

Q1recall

Where do the atoms in a new substance come from?

  1. A the change makes them from nothing as it happens
  2. B from the heat that the change gives off
  3. C from the substances that were there before
Answer

Key: C — from the substances that were there before

No atom is made from nothing.
No atom vanishes.
So the atoms in a new substance come from the substances that were there before.

Feedback per option

  • A No atom is made from nothing.
  • B Heat is not made of atoms; the atoms were there before the change.
  • C The atoms in a new substance come from the substances that were there before.
Q2recall

Two or more atoms joined together make one particle. What is that particle called?

  1. A an element
  2. B a molecule
  3. C a mixture
Answer

Key: B — a molecule

Two or more atoms joined together make one particle.
That particle is called a molecule.

Feedback per option

  • A An element is a substance made of one kind of atom; the particle of joined atoms is a molecule.
  • B Two or more atoms joined together make one particle called a molecule.
  • C A mixture is substances mingled, not joined; the particle of joined atoms is a molecule.
Q3recall

A popsicle melts into a puddle. Are the particles in the puddle the same particles that were in the popsicle?

  1. A yes
  2. B no
Answer

Key: A — yes

Melting changes the state of a substance.
The particles are the same particles, arranged or moving differently.
So the puddle holds the same particles as the popsicle.

Feedback per option

  • A Melting changes the state, not the particles: the same particles, moving more freely.
  • B No new particles form when a popsicle melts; the same particles are there, moving more freely.
Q4fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: A — yes

Before: two pairs of small dark circles and two single gray circles.
After: each gray circle is joined to two small dark circles.
The atoms changed partners, so this is a chemical reaction.

Feedback per option

  • A Before, the small dark circles were in pairs and the gray circles stood alone; after, each gray circle is joined to two small dark circles: new partners, a chemical reaction.
  • B Look at the pairs: before, the small dark circles were paired with each other; after, each is joined to a gray circle. The partners changed.
Q5fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: B — no

Before: four groups, each one large open circle joined to two small dark circles.
After: the same four groups, in new places.
No atom changed partners, so this is not a chemical reaction.

Feedback per option

  • A Look at each group: after, it is still one large open circle joined to two small dark circles, the same as before. Moving is not changing partners.
  • B Every group after is still one large open circle joined to two small dark circles, the same as before; the groups only moved.
Q6fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: B — no

Before: three groups of a gray circle between two large open circles, and two pairs of small dark circles.
After: the same groups and pairs, in new places.
No atom changed partners, so this is not a chemical reaction.

Feedback per option

  • A Look at each group: the three-atom groups and the pairs of small dark circles are the same after as before. Moving is not changing partners.
  • B The three-atom groups and the pairs of small dark circles are the same after as before; they only moved.
Q7fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: A — yes

Before: pairs of gray circles and pairs of small dark circles.
After: each gray circle is joined to a small dark circle.
The atoms changed partners, so this is a chemical reaction.

Feedback per option

  • A Before, gray circles were joined to gray and small dark to small dark; after, each gray circle is joined to a small dark circle: new partners.
  • B Before, like was joined to like; after, each gray circle is joined to a small dark circle. The partners changed.
Q8fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: A — yes

Before: four single gray circles and two pairs of large open circles.
After: each gray circle is joined to one large open circle.
The atoms changed partners, so this is a chemical reaction.

Feedback per option

  • A Before, the gray circles stood alone and the large open circles came in pairs; after, each gray circle is joined to a large open circle.
  • B Before, the gray circles stood alone; after, each is joined to a large open circle that left its pair. The partners changed.
Q9fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: B — no

Before: five pairs of small dark circles.
After: the same five pairs, in new places.
No atom changed partners, so this is not a chemical reaction.

Feedback per option

  • A Look at each pair: after, it is still a pair of small dark circles, the same as before. Moving is not changing partners.
  • B Every pair after is still a pair of small dark circles, the same as before; the pairs only moved.
Q10fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: B — no

Before: three groups of three kinds joined, and three single large open circles.
After: the same groups and singles, in new places.
No atom changed partners, so this is not a chemical reaction.

Feedback per option

  • A Look at each group: the three-kind groups and the single large open circles are the same after as before. Moving is not changing partners.
  • B The three-kind groups and the single large open circles are the same after as before; they only moved.
Q11fluency

Each size and shade of circle is a different kind of atom, and touching circles are joined. The two boxes show the atoms before and after a change. Did the atoms change partners?

beforeafterDid the atoms change partners?
  1. A yes
  2. B no
Answer

Key: A — yes

Before: two groups of a large open circle joined to two small dark circles, and two single gray circles.
After: each large open circle is joined to a gray circle, and the small dark circles are in pairs.
The atoms changed partners, so this is a chemical reaction.

Feedback per option

  • A Before, each large open circle was joined to two small dark circles; after, it is joined to a gray circle, and the small dark circles pair up: new partners.
  • B Before, each large open circle was joined to two small dark circles; after, it is joined to a gray circle. The partners changed.
Q12misconception

Eitan says: "Charcoal burning is a chemical reaction, because the carbon atoms join new partners." Is Eitan correct?

  1. A yes
  2. B no
Answer

Key: A — yes

When charcoal burns, each carbon atom joins two oxygen atoms from the air.
The atoms changed partners, and carbon dioxide is a new substance.
So charcoal burning is a chemical reaction, and Eitan is correct.

Feedback per option

  • A Each carbon atom lets go of the charcoal and joins two oxygen atoms from the air: new partners, a new substance, a chemical reaction.
  • B Eitan's reason is the test itself: the carbon atoms join new partners, oxygen atoms, and carbon dioxide is a new substance, so this is a chemical reaction.
Q13misconception

Delphine says: "Boiling water is a chemical reaction, because bubbles form." Is Delphine correct?

  1. A yes
  2. B no
Answer

Key: B — no

The bubbles in boiling water are water molecules that have spread out into a gas.
Each water molecule is still one oxygen atom joined to two hydrogen atoms.
No atom changed partners, so boiling is not a chemical reaction, and Delphine is not correct.

Feedback per option

  • A Bubbles are not the test. The bubbles are water molecules spread out into a gas; each is still one oxygen atom joined to two hydrogen atoms: no partner changed.
  • B The bubbles are water molecules that spread out into a gas; every molecule keeps its atoms, so no atom changed partners and boiling is not a chemical reaction.
Your note · lesson 2: A chemical reaction rearranges atoms
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 3 of 8Author: could do without a video196 words · about 1:38

Reactants and products: the word equation

MAT-067 · Reactants and products — Label the reactants and products in a chemical equation.

Script
SayScreen
Methane, the main gas in natural gas, burns on a kitchen stove.[a stove flame]
Methane and oxygen go in; carbon dioxide and water come out.[two boxes flow into the flame; two flow out]
A chemist writes this on one line with an arrow: which substances go left, and which go right?[an empty strip with an arrow; question mark]
The substances that go in go on the left, and the substances that come out go on the right.[the left and right halves of the strip light in turn]
Methane and oxygen go into the reaction, so they go on the left.[methane + oxygen slide onto the left of the strip]
The substances that go into a reaction are called the reactants.[chip: REACTANTS over the left half]
Carbon dioxide and water come out, so they go on the right.[carbon dioxide + water slide onto the right]
The substances that come out of a reaction are called the products.[chip: PRODUCTS over the right half]
The arrow means “react to make”.[the arrow glows; label: react to make]
A plus sign reads “and”.[the plus signs glow; label: and]
This line, written in words, is called a word equation.[chip: WORD EQUATION under the strip]
The whole line reads: methane and oxygen react to make carbon dioxide and water.[each word lights as it is spoken]
Now consider iron rusting: iron and oxygen are the reactants, iron oxide the product.[strip: iron + oxygen → iron oxide; labels]
The arrow is not an equals sign: the products are new substances.[a crossed-out line with an equals sign]
So, a word equation writes the reactants on the left, an arrow that reads “react to make”, and the products on the right.[the rule slide: the finished methane strip; chips REACTANTS, REACT TO MAKE, PRODUCTS; nothing else printed]
Okay, now your turn.[closing screen: bullets — • Reactants on the left • The arrow means “react to make” • Products on the right]

“Okay, now your turn.” — the attached question

video

In a word equation, what does the arrow between the reactants and the products read?

  1. A react to make
  2. B is the same as
  3. C and
Answer

Key: A — react to make

A word equation writes the reactants, an arrow, and the products.
The arrow means “react to make”.
So methane and oxygen react to make carbon dioxide and water.

Feedback per option

  • A The arrow means “react to make”: methane and oxygen react to make carbon dioxide and water.
  • B The arrow is not an equals sign; the products are new substances, not the same as the reactants.
  • C The plus sign reads “and”; the arrow means “react to make”.

Quiz after the video — the mastery check, 12 items

Q1recall

In a chemical reaction, what do the atoms do?

  1. A they let go of old partners and join new ones
  2. B they move to new places and keep their partners
  3. C they vanish and new atoms appear
Answer

Key: A — they let go of old partners and join new ones

In a chemical reaction the atoms let go of their old partners.
They join new partners.
So new substances form.

Feedback per option

  • A In a chemical reaction the atoms let go of their old partners and join new ones, so new substances form.
  • B Keeping the same partners is melting or dissolving, not a chemical reaction.
  • C No atom vanishes and none is made from nothing; the atoms change partners.
Q2fluency

zinc + sulfur → zinc sulfide. Which of these is a reactant?

  1. A sulfur
  2. B zinc sulfide
Answer

Key: A — sulfur

The reactants are written on the left of the arrow.
Sulfur is on the left.
So sulfur is a reactant.

Feedback per option

  • A Sulfur is on the left of the arrow: it goes in, so it is a reactant.
  • B Zinc sulfide is on the right of the arrow, so it comes out: it is the product.
Q3fluency

sodium + chlorine → sodium chloride. Which of these is the product?

  1. A sodium
  2. B sodium chloride
Answer

Key: B — sodium chloride

The products are written on the right of the arrow.
Sodium chloride is on the right.
So sodium chloride is the product.

Feedback per option

  • A Sodium is on the left of the arrow, so it goes in: it is a reactant.
  • B Sodium chloride is on the right of the arrow: it comes out, so it is the product.
Q4fluency

copper + oxygen → copper oxide. Which of these is the product?

  1. A oxygen
  2. B copper oxide
Answer

Key: B — copper oxide

The products are written on the right of the arrow.
Copper oxide is on the right.
So copper oxide is the product.

Feedback per option

  • A Oxygen is on the left of the arrow, so it goes in: it is a reactant.
  • B Copper oxide is on the right of the arrow: it comes out, so it is the product.
Q5fluency

magnesium + oxygen → magnesium oxide. Which of these is a reactant?

  1. A magnesium
  2. B magnesium oxide
Answer

Key: A — magnesium

The reactants are written on the left of the arrow.
Magnesium is on the left.
So magnesium is a reactant.

Feedback per option

  • A Magnesium is on the left of the arrow: it goes in, so it is a reactant.
  • B Magnesium oxide is on the right of the arrow, so it comes out: it is the product.
Q6fluency

hydrogen + chlorine → hydrogen chloride. Which of these is a reactant?

  1. A chlorine
  2. B hydrogen chloride
Answer

Key: A — chlorine

The reactants are written on the left of the arrow.
Chlorine is on the left.
So chlorine is a reactant.

Feedback per option

  • A Chlorine is on the left of the arrow: it goes in, so it is a reactant.
  • B Hydrogen chloride is on the right of the arrow: it comes out, so it is the product.
Q7fluency

sulfur + oxygen → sulfur dioxide. Which of these is the product?

  1. A sulfur
  2. B sulfur dioxide
Answer

Key: B — sulfur dioxide

The products are written on the right of the arrow.
Sulfur dioxide is on the right.
So sulfur dioxide is the product.

Feedback per option

  • A Sulfur is on the left of the arrow: it goes in, so it is a reactant.
  • B Sulfur dioxide is on the right of the arrow: it comes out, so it is the product.
Q8transfer

Zinc and oxygen react and make zinc oxide. Which line writes this as a word equation?

  1. A zinc + oxygen → zinc oxide
  2. B zinc oxide → zinc + oxygen
  3. C zinc + zinc oxide → oxygen
Answer

Key: A — zinc + oxygen → zinc oxide

Zinc and oxygen go in, so they are the reactants and stand on the left.
Zinc oxide comes out, so it is the product and stands on the right.
The arrow between them reads “react to make”: zinc + oxygen → zinc oxide.

Feedback per option

  • A Zinc and oxygen go in, on the left; zinc oxide comes out, on the right.
  • B This line puts what comes out on the left; the reactants, zinc and oxygen, belong on the left.
  • C Zinc oxide comes out of the reaction, so it belongs on the right, not among the reactants.
Q9misconception

Wynn says: "The arrow in a word equation means equals, so the same substances sit on both sides." Is Wynn correct?

  1. A yes
  2. B no
Answer

Key: B — no

The arrow in a word equation reads “react to make”.
The products are new substances, made from the reactants.
So different substances sit on the two sides, and Wynn is not correct.

Feedback per option

  • A The arrow is not an equals sign: it means “react to make”, and the products are new substances, so the two sides name different substances.
  • B The arrow means “react to make”; the products are new substances, so the two sides name different substances and Wynn is not correct.
Q10term

In a reaction, the substances that go in, like the iron and the oxygen when iron rusts, are written on the left. What are these substances called?

Typed answer

Answer

Accepted: reactants · the reactants · reactant · a reactant

The iron and the oxygen go into the reaction.
The substances that go into a reaction are called the reactants.
Q11term

In a reaction, the substances that come out, like the iron oxide when iron rusts, are written on the right. What are these substances called?

Typed answer

Answer

Accepted: products · the products · product · a product

The iron oxide comes out of the reaction.
The substances that come out of a reaction are called the products.
Q12term

A chemist writes a reaction as one line of words with an arrow in the middle. What is a line like this called?

Typed answer

Answer

Accepted: word equation · a word equation · the word equation · an equation · equation

The line writes what goes in, an arrow, and what comes out, all in words.
A line like this is called a word equation.
Your note · lesson 3: Reactants and products: the word equation
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 4 of 8Author: could do without a video189 words · about 1:34

Which elements take part: read the symbols

MAT-071 · Identify the elements in a reaction using the periodic table — Use the periodic table to identify every element involved in a given chemical reaction.

Script
SayScreen
A chemist writes methane burning with formulas: CH₄ plus 2O₂ react to make CO₂ plus 2H₂O.[the word equation strip; the formula form appears under it]
Each letter group is a chemical symbol, and each symbol names one element, so the symbols tell us which elements take part.[the letters glow]
To find every element in a reaction, there are three steps to follow.[1, 2, 3 as bold numbers]
One: read each capital letter, with any small letter after it, as one symbol.[C, H, O, C, O, H, O underlined in turn]
Two: look each symbol up on the periodic table: C is carbon, H is hydrogen, O is oxygen.[the periodic table; the three boxes ringed]
Three: write each element down once, however many times its symbol appears.[the list: carbon, hydrogen, oxygen]
So methane burning uses three elements: carbon, hydrogen and oxygen.[chip: 3 ELEMENTS]
The numbers are not symbols: a number in front counts particles, and a small low number counts atoms.[the 2 and the 4 boxed; label: not elements]
Now consider magnesium burning: 2Mg plus O₂ react to make 2MgO.[magnesium + oxygen → magnesium oxide; the formula form]
Mg is one symbol, magnesium, and O is oxygen.[Mg underlined; O underlined]
Watch out for one capital or two: CO is carbon and oxygen, but Co is one element, cobalt.[CO with two underlines; Co with one]
So, to find every element in a reaction, read each symbol, look it up on the periodic table, and write each element once.[the rule slide: the methane equation with C, H and O underlined, the periodic table beside it with the three boxes ringed; nothing else printed]
Okay, now your turn.[closing screen: bullets — • Read each symbol • Look it up on the periodic table • Write each element once]

“Okay, now your turn.” — the attached question

video

Methane burns: CH₄ + 2O₂ → CO₂ + 2H₂O. How many elements take part?

  1. A 2 elements
  2. B 3 elements
  3. C 4 elements
Answer

Key: B — 3 elements

The symbols in CH₄ + 2O₂ → CO₂ + 2H₂O are C, H and O.
Each element is written once, however often its symbol appears.
So three elements take part.

Feedback per option

  • A Three symbols appear: C, H and O; that is three elements, not two.
  • B C is carbon, H is hydrogen, O is oxygen: three elements, each written once.
  • C The numbers in the equation are not symbols; only C, H and O name elements.

Quiz after the video — the mastery check, 12 items

Q1recall

Count the capital letters in HBr. How many elements does HBr name?

  1. A one element
  2. B two elements
Answer

Key: B — two elements

Every capital letter starts a new chemical symbol.
HBr has two capital letters, the H and the B.
So HBr names two elements, hydrogen and bromine.

Feedback per option

  • A HBr has two capital letters, H and B, so it names two elements: hydrogen and bromine.
  • B Every capital letter starts a new symbol. H and Br are two symbols: hydrogen and bromine.
Q2recall

On the periodic table, what does one box stand for?

  1. A one element
  2. B one atom
  3. C one compound
Answer

Key: A — one element

The periodic table is a chart of every known element.
Each element has one box.
So one box stands for one element.

Feedback per option

  • A The periodic table is a chart of every known element, one box per element.
  • B A box stands for an element, not a single atom; every atom of that element belongs to the box.
  • C Compounds are not on the periodic table; each box is one element.
Q3recall

In the formula SO₂, what does the small 2 count?

  1. A the elements in the particle
  2. B sulfur atoms in one particle
  3. C oxygen atoms in one particle
Answer

Key: C — oxygen atoms in one particle

A subscript counts the atoms of the element just before it.
The 2 comes just after the O.
So the 2 counts 2 oxygen atoms in one particle.

Feedback per option

  • A A subscript counts atoms, not elements; the symbols name the elements.
  • B The 2 comes just after the O, not the S, so it counts oxygen atoms.
  • C A subscript counts the atoms of the element just before it: 2 oxygen atoms in one particle.
Q4scaffold

A soft, silvery metal burns in a yellow-green gas: 2Na + Cl₂ → 2NaCl. Read each capital letter with any small letter after it. Which symbols appear?

  1. A N, a, C and l, as four symbols
  2. B Na, Cl and the 2
  3. C Na and Cl
Answer

Key: C — Na and Cl

A symbol is a capital letter with any small letter after it.
Na is one symbol and Cl is one symbol.
The 2 counts particles, so the symbols are Na and Cl.

Feedback per option

  • A A small letter after a capital belongs to the same symbol: Na is one symbol and Cl is one symbol.
  • B The 2 is a number in front; it counts particles and is not a symbol.
  • C Two symbols: Na, a capital N with a small a; and Cl, a capital C with a small l.
Q5scaffold

Part of the periodic table is supplied. Look up Na. Which element is Na?

1Hhydrogen3Lilithium4Beberyllium11Nasodium12Mgmagnesium19Kpotassium20Cacalcium21Scscandium22Tititanium12341234part of the periodic table:groups 1–4, periods 1–42Na + Cl₂ → 2NaCl

Typed answer

Answer

Accepted: sodium

Find the box marked Na on the periodic table.
The box is sodium, atomic number 11.
So Na is sodium.
Q6scaffold

Part of the periodic table is supplied. Look up Cl. Which element is Cl?

2Hehelium5Bboron6Ccarbon7Nnitrogen8Ooxygen9Ffluorine10Neneon13Alaluminum14Sisilicon15Pphosphorus16Ssulfur17Clchlorine18Arargon131415161718123part of the periodic table: groups 13–18, periods 1–32Na + Cl₂ → 2NaCl

Typed answer

Answer

Accepted: chlorine

Find the box marked Cl on the periodic table.
The box is chlorine, atomic number 17.
So Cl is chlorine.
Q7scaffold

Na and Cl each appear twice in 2Na + Cl₂ → 2NaCl. Write each element once. How many elements take part?

Typed answer

Answer

Accepted: 2 · two · 2 elements

Na is sodium, and Cl is chlorine.
Each element is written once, however many times its symbol appears.
So two elements take part: sodium and chlorine.
Q8bare

Part of the periodic table is supplied. Zn + S → ZnS. List every element that takes part.

5Bboron6Ccarbon7Nnitrogen8Ooxygen9Ffluorine13Alaluminum14Sisilicon15Pphosphorus16Ssulfur17Clchlorine30Znzinc31Gagallium32Gegermanium33Asarsenic34Seselenium35Brbromine121314151617234part of the periodic table: groups 12–17, periods 2–4Zn + S → ZnS

Typed answer

Answer

Accepted: zinc, sulfur · zinc and sulfur · zinc, and sulfur · zinc sulfur · sulfur, zinc · sulfur and zinc · sulfur, and zinc · sulfur zinc

The symbols are Zn and S.
On the periodic table, Zn is zinc and S is sulfur.
So two elements take part: zinc and sulfur.
In words, Zn + S → ZnS is zinc + sulfur → zinc sulfide.
Q9bare

Part of the periodic table is supplied. 2Cu + O₂ → 2CuO. List every element that takes part.

5Bboron6Ccarbon7Nnitrogen8Ooxygen13Alaluminum14Sisilicon15Pphosphorus16Ssulfur29Cucopper30Znzinc31Gagallium32Gegermanium33Asarsenic34Seselenium111213141516234part of the periodic table: groups 11–16, periods 2–42Cu + O₂ → 2CuO

Typed answer

Answer

Accepted: copper, oxygen · copper and oxygen · copper, and oxygen · copper oxygen · oxygen, copper · oxygen and copper · oxygen, and copper · oxygen copper

The symbols are Cu and O.
On the periodic table, Cu is copper and O is oxygen.
So two elements take part: copper and oxygen.
In words, 2Cu + O₂ → 2CuO is copper + oxygen → copper oxide.
Q10bare

Part of the periodic table is supplied. 2K + 2H₂O → 2KOH + H₂. List every element that takes part.

1Hhydrogen3Lilithium4Beberyllium11Nasodium12Mgmagnesium19Kpotassium20Cacalcium21Scscandium22Tititanium12341234part of the periodic table:groups 1–4, periods 1–46Ccarbon7Nnitrogen8Ooxygen9Ffluorine14Sisilicon15Pphosphorus16Ssulfur17Clchlorine1415161723part of the periodic table:groups 14–17, periods 2–32K + 2H₂O → 2KOH + H₂

Typed answer

Answer

Accepted: potassium, hydrogen, oxygen · potassium and hydrogen and oxygen · potassium, and hydrogen, and oxygen · potassium hydrogen oxygen · potassium, hydrogen and oxygen · potassium, hydrogen, and oxygen · potassium, oxygen, hydrogen · potassium and oxygen and hydrogen · potassium, and oxygen, and hydrogen · potassium oxygen hydrogen · potassium, oxygen and hydrogen · potassium, oxygen, and hydrogen · hydrogen, potassium, oxygen · hydrogen and potassium and oxygen · hydrogen, and potassium, and oxygen · hydrogen potassium oxygen · hydrogen, potassium and oxygen · hydrogen, potassium, and oxygen · hydrogen, oxygen, potassium · hydrogen and oxygen and potassium · hydrogen, and oxygen, and potassium · hydrogen oxygen potassium · hydrogen, oxygen and potassium · hydrogen, oxygen, and potassium · oxygen, potassium, hydrogen · oxygen and potassium and hydrogen · oxygen, and potassium, and hydrogen · oxygen potassium hydrogen · oxygen, potassium and hydrogen · oxygen, potassium, and hydrogen · oxygen, hydrogen, potassium · oxygen and hydrogen and potassium · oxygen, and hydrogen, and potassium · oxygen hydrogen potassium · oxygen, hydrogen and potassium · oxygen, hydrogen, and potassium

The symbols are K, H and O.
On the periodic table, K is potassium, H is hydrogen and O is oxygen.
Each is written once, so three elements take part.
In words: potassium + water → potassium hydroxide + hydrogen.
Q11transfer

Part of the periodic table is supplied. CO is a poisonous gas, and Co is a metal used in some magnets. How many elements does each name?

27Cocobalt28Ninickel29Cucopper30Znzinc91011124part of the periodic table:groups 9–12, period 45Bboron6Ccarbon7Nnitrogen8Ooxygen13Alaluminum14Sisilicon15Pphosphorus16Ssulfur1314151623part of the periodic table:groups 13–16, periods 2–3CO and Co
  1. A both name two elements
  2. B CO names two elements and Co names one
  3. C CO names one element and Co names two elements
Answer

Key: B — CO names two elements and Co names one

Every capital letter starts a new symbol.
CO has two capitals: C, carbon, and O, oxygen: two elements.
Co has one capital and a small o: one symbol, cobalt: one element.

Feedback per option

  • A Co has one capital letter and a small o, so it is one symbol: cobalt.
  • B CO is two capitals, C and O, carbon and oxygen; Co is one capital with a small o, one symbol, cobalt.
  • C CO has two capitals, C and O, so it is two symbols; Co has one capital and a small o, so it is one: the other way round.
Q12misconception

Gus says: "In CO₂, the capital O starts a second symbol, so CO₂ names two elements: carbon and oxygen." Is Gus correct?

  1. A yes
  2. B no
Answer

Key: A — yes

Every capital letter starts a new chemical symbol.
CO₂ has two capitals, C and O: carbon and oxygen.
The 2 counts oxygen atoms, not elements, so Gus is correct.

Feedback per option

  • A Every capital letter starts a new symbol: C is carbon and O is oxygen, two elements; the small 2 counts atoms, not elements.
  • B Gus is right: the capital O starts a second symbol, so CO₂ names carbon and oxygen; the small 2 counts oxygen atoms, not a third element.
Your note · lesson 4: Which elements take part: read the symbols
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 5 of 8Author: could do without a video170 words · about 1:25

The law of conservation of mass

MAT-069 · The law of conservation of mass — State the law of conservation of mass.

Script
SayScreen
Suppose a lidded jar holds vinegar and a packet of baking soda, and the balance reads 250.0 grams.[the lidded jar on the balance; readout 250.0 g]
When the jar tips, the vinegar runs onto the baking soda, the mixture fizzes, and the jar fills with gas.[the jar tips; bubbles rise]
Back on the balance it still reads 250.0 grams: why did the mass not change?[readout 250.0 g; question mark]
Every atom is still in the jar, and each one keeps its mass.[the jar; chip: EVERY ATOM STILL HERE]
A gas is matter, so it has mass.[chip: A GAS HAS MASS]
Baking soda and vinegar react to make sodium acetate, water and carbon dioxide.[strip: baking soda + vinegar → sodium acetate + water + carbon dioxide]
Let's zoom in: the atoms only swap partners, so every atom that was there before is still there after.[atoms regroup inside the jar; none leaves]
Each atom keeps its own mass, and the lid keeps the carbon dioxide molecules inside.[gas molecules bounce under the lid]
So the total mass of the products equals the total mass of the reactants.[the line appears: total mass of the products = total mass of the reactants]
This rule is called the law of conservation of mass.[the rule slide: the two readouts, 250.0 g before and 250.0 g after; chip LAW OF CONSERVATION OF MASS; nothing else printed]
So in the jar, every atom stayed inside with its mass, and the balance still reads 250.0 grams.[the jar; readout 250.0 g]
Okay, now your turn.[closing screen: one line — "The total mass of the products equals the total mass of the reactants: the law of conservation of mass."]

“Okay, now your turn.” — the attached question

video

Vinegar fizzes with baking soda inside a lidded jar on a balance that read 250.0 g before. What does the balance read after?

  1. A less than 250.0 g
  2. B 250.0 g
  3. C more than 250.0 g
Answer

Key: B — 250.0 g

The atoms only swap partners inside the jar.
The lid keeps every atom in, and each keeps its mass.
So the jar still reads 250.0 g.

Feedback per option

  • A The gas stays in the lidded jar with its mass, so the reading does not fall.
  • B Every atom stays in the jar and keeps its mass, so the reading stays at 250.0 g.
  • C Nothing comes into the lidded jar, so the reading does not rise.

Quiz after the video — the mastery check, 11 items

Q1recall

When iron rusts, where were the oxygen atoms in the rust before the change?

  1. A in the air
  2. B inside the iron atoms
  3. C nowhere at all
Answer

Key: A — in the air

The atoms in a new substance come from the substances that were there before.
The air around the iron holds oxygen.
So the oxygen atoms in the rust were in the air before the change.

Feedback per option

  • A The atoms in a new substance come from the substances that were there before: the oxygen atoms were in the air.
  • B An iron atom holds no oxygen atoms; the oxygen came from outside the iron.
  • C No atom is made from nothing; the oxygen atoms were in the air already.
Q2recall

Two substances inside a sealed jar change into a new substance. What happens to the total mass in the jar?

  1. A it goes up
  2. B it stays the same
  3. C it goes down
Answer

Key: B — it stays the same

The jar is sealed, so nothing comes in and nothing leaves.
When substances change inside a sealed jar, the total mass stays the same.

Feedback per option

  • A Nothing came in through the seal, so the mass cannot go up.
  • B When substances change inside a sealed jar, the total mass in the jar stays the same.
  • C Nothing left through the seal, so the mass cannot go down.
Q3recall

Carbon dioxide gas fills a jar. Does the gas have mass?

  1. A yes
  2. B no
Answer

Key: A — yes

A gas is matter.
Matter has mass and takes up space.
So the carbon dioxide gas has mass.

Feedback per option

  • A A gas is matter: it has mass and takes up space.
  • B You cannot see the gas, but a gas is matter: it has mass and takes up space.
Q4what

In a chemical reaction, which sentence is true of the total mass?

  1. A The total mass of the products is less than the total mass of the reactants.
  2. B The total mass of the products is more than the total mass of the reactants.
  3. C The total mass of the products equals the total mass of the reactants.
Answer

Key: C — The total mass of the products equals the total mass of the reactants.

Every atom that was there before is still there after.
Each atom keeps its own mass.
So the total mass of the products equals the total mass of the reactants.

Feedback per option

  • A A gas has mass like any matter; the total mass does not fall.
  • B New substances are the same atoms in new partners; no mass is added.
  • C Every atom that was there before is still there after, and each keeps its mass: the totals are equal.
Q5what

Suppose a sealed bottle holds water and a fizzing tablet. The tablet fizzes until it is gone, and the bottle stays sealed. Compared with before, what is the bottle's mass now?

  1. A less than before
  2. B the same as before
  3. C more than before
Answer

Key: B — the same as before

The atoms only swapped partners inside the bottle.
The seal kept every atom inside, the gas included.
Each atom keeps its own mass, so the bottle's mass is the same.

Feedback per option

  • A The gas from the fizz is still in the sealed bottle, and it has mass.
  • B Every atom is still in the sealed bottle, and each keeps its mass: the total is the same.
  • C Nothing came into the sealed bottle, so no mass was added.
Q6why

Suppose a sealed carton of milk is left in a warm room, and the milk turns sour: a chemical change. The carton's mass does not change. Explain why.

Starter: In the reaction, the atoms only…

Answer

Model answer · ['the atoms only swap partners, so every atom is still there', 'the carton is sealed, so nothing left or came in', 'each atom keeps its own mass, so the total mass is the same'] points

In the reaction, the atoms only swap partners.
Every atom that was there before is still there after.
The carton is sealed, so no atom left and none came in.
Each atom keeps its own mass.
So the total mass of the products equals the total mass of the reactants, and the carton has the same mass.
Q7misconception

Halle says: "The sealed jar's mass should go down when the fizz makes a gas, because a gas has no mass." Is Halle correct?

  1. A yes
  2. B no
Answer

Key: B — no

A gas is matter, and matter has mass.
The carbon dioxide molecules are made of atoms that were in the jar before, each with its own mass.
The lid keeps them in, so the mass stays the same, and Halle is not correct.

Feedback per option

  • A Halle's reason is wrong: a gas is matter, so its molecules have mass; the lid keeps them in the jar, and the total mass stays the same.
  • B A gas is matter, so its molecules have mass; the lid keeps them in the jar, so the total mass stays the same and Halle is not correct.
Q8misconception

Ivo says: "Each atom keeps its own mass, and every atom is still in the sealed jar, so the total mass cannot change." Is Ivo correct?

  1. A yes
  2. B no
Answer

Key: A — yes

In a reaction the atoms only swap partners, so every atom is still there.
Each atom keeps its own mass.
So the total mass cannot change, and Ivo is correct.

Feedback per option

  • A That is the reason behind the law of conservation of mass: the same atoms, each with the same mass, so the same total.
  • B Ivo is right: the same atoms are still in the jar, each with the same mass, so the total cannot change.
Q9transfer

A sealed bag holds bread dough. The yeast in the dough makes carbon dioxide gas, and the dough puffs up. What happens to the bag's mass?

  1. A it goes up
  2. B it stays the same
  3. C it goes down
Answer

Key: B — it stays the same

The carbon dioxide is made of atoms that were in the dough before.
The bag is sealed, so every atom stays inside.
Each atom keeps its own mass, so the bag's mass stays the same.

Feedback per option

  • A Bigger is not more mass; the same atoms fill more space.
  • B The gas came from atoms already in the dough, and the sealed bag keeps every atom in: the total mass is the same.
  • C The gas left the dough but not the sealed bag; every atom is still inside.
Q10fluency

In a sealed flask, 8.0 g of reactants react completely and nothing else is added. What is the total mass of the products, in g?

Typed answer

Answer

Accepted: 8.0 g · 8.0 · 8.0 grams · 8.0g · 8 g · 8 · 8 grams

The total mass of the products equals the total mass of the reactants.
The reactants had a mass of 8.0 g.
So the products have a total mass of 8.0 g.
Q11term

In a chemical reaction, the total mass of the products equals the total mass of the reactants. What is this rule called?

Typed answer

Answer

Accepted: law of conservation of mass · the law of conservation of mass · conservation of mass · the conservation of mass

The total mass is kept, or conserved, through the reaction.
This rule is called the law of conservation of mass.
Your note · lesson 5: The law of conservation of mass
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 6 of 8Author: definitely a video200 words · about 1:40

Work out a missing mass, and the open-dish trap

MAT-069b · Apply conservation of mass to a reaction — Calculate the mass of the products of a reaction given the total mass of the reactants.

Script
SayScreen
Suppose you heat 10.0 grams of limestone in a lidded jar, on a balance zeroed with the jar empty.[the lidded jar on the balance; readout 10.0 g]
It splits into 5.6 grams of calcium oxide and carbon dioxide gas, whose mass we want.[strip: calcium carbonate → calcium oxide + carbon dioxide; question mark over the gas]
The law of conservation of mass says the total mass of the products equals the total mass of the reactants.[the law in one line]
Here, mass of calcium oxide plus mass of carbon dioxide equals mass of calcium carbonate.[the line builds word by word]
Make the unknown the subject: mass of carbon dioxide equals mass of calcium carbonate minus mass of calcium oxide.[the line rearranges]
Substitute and calculate: 10.0 grams minus 5.6 grams is 4.4 grams.[10.0 g − 5.6 g = 4.4 g]
Now suppose you heat the same limestone in an open dish, zeroed the same way: the reading falls to 5.6 grams.[the open dish on the balance; readout falls from 10.0 g to 5.6 g]
Where did the 4.4 grams go?[question mark over the readout]
It floated away as carbon dioxide gas: the missing 4.4 grams is in the air.[carbon dioxide molecules float up and off; molecules in the air above]
No mass was destroyed; every atom is somewhere.[chip: NOTHING DESTROYED]
Steel wool rusting on an open pan gains mass.[a pad on a balance; readout climbs]
Oxygen joined on; no mass was created.[oxygen pairs land on the pad]
So, to find a missing mass, write the law in the reaction's own substances, make the unknown the subject, substitute, and calculate.[the rule slide: the two balances, the lidded jar at 10.0 g and the open dish at 5.6 g; chip NOTHING DESTROYED; nothing else printed]
Okay, now your turn.[closing screen: bullets — • Write the law in the reaction's own substances • Make the unknown the subject • Substitute • Calculate]

“Okay, now your turn.” — the attached question

video

Limestone is heated in an open dish on a zeroed balance, and carbon dioxide gas leaves. What does the balance reading do?

  1. A it falls
  2. B it stays the same
  3. C it rises
Answer

Key: A — it falls

The reaction makes carbon dioxide gas, which has mass.
The dish is open, so the gas floats away.
So the reading falls.

Feedback per option

  • A The carbon dioxide gas floats out of the open dish with its mass, so the reading falls.
  • B The reading stays the same only in a lidded jar; the open dish lets the gas leave.
  • C A gas leaves; none comes in, so the reading does not rise.

Quiz after the video — the mastery check, 13 items

Q1recall

In a chemical reaction, how does the total mass of the products compare with the total mass of the reactants?

  1. A it is less
  2. B it is the same
  3. C it is more
Answer

Key: B — it is the same

Every atom that was there before is still there after.
Each atom keeps its own mass.
So the total mass of the products equals the total mass of the reactants.

Feedback per option

  • A No atom vanishes, so the total cannot fall.
  • B The total mass of the products equals the total mass of the reactants: the law of conservation of mass.
  • C No atom is made from nothing, so the total cannot rise.
Q2recall

A balance shows 5.6 for a heap of white powder. Which unit belongs after the number?

  1. A g
  2. B mL
  3. C cm³
Answer

Key: A — g

A balance measures mass.
Mass is measured in grams, written g.
So the reading is 5.6 g.

Feedback per option

  • A A balance measures mass, and mass is measured in grams, g.
  • B mL is a unit of volume, not mass.
  • C cm³ is a unit of volume, not mass.
Q3scaffold

12.0 g of magnesium burns in oxygen and makes 19.9 g of magnesium oxide, which holds every atom that reacted. Write the law in this reaction's substances. Which line is right?

  1. A mass of magnesium + mass of oxygen = mass of magnesium oxide
  2. B mass of magnesium = mass of oxygen + mass of magnesium oxide
  3. C mass of magnesium × mass of oxygen = mass of magnesium oxide
Answer

Key: A — mass of magnesium + mass of oxygen = mass of magnesium oxide

The reactants are magnesium and oxygen; the product is magnesium oxide.
The total mass of the products equals the total mass of the reactants.
So mass of magnesium + mass of oxygen = mass of magnesium oxide.

Feedback per option

  • A Two reactants go in, one product comes out: the two reactant masses add up to the product's mass.
  • B Oxygen is a reactant, not a product; it belongs on the reactants' side with the magnesium.
  • C Masses add; they are never multiplied.
Q4scaffold

Make the mass of oxygen the subject of your line for magnesium burning. Which line is right?

  1. A mass of oxygen = mass of magnesium − mass of magnesium oxide
  2. B mass of oxygen = mass of magnesium oxide + mass of magnesium
  3. C mass of oxygen = mass of magnesium oxide − mass of magnesium
Answer

Key: C — mass of oxygen = mass of magnesium oxide − mass of magnesium

Start from mass of magnesium + mass of oxygen = mass of magnesium oxide.
Take the mass of magnesium away from both sides.
So mass of oxygen = mass of magnesium oxide − mass of magnesium.

Feedback per option

  • A This takes the larger mass away from the smaller; the oxygen is the product's mass minus the magnesium's.
  • B Adding gives more than the product's whole mass; the oxygen is what is left when the magnesium is taken away.
  • C Take the mass of magnesium away from both sides: the oxygen's mass is the product's mass minus the magnesium's.
Q5scaffold

Substitute the values for magnesium burning. Which line is right?

  1. A mass of oxygen = 12.0 g − 19.9 g
  2. B mass of oxygen = 19.9 g − 12.0 g
  3. C mass of oxygen = 19.9 g + 12.0 g
Answer

Key: B — mass of oxygen = 19.9 g − 12.0 g

The line is mass of oxygen = mass of magnesium oxide − mass of magnesium.
The magnesium oxide is 19.9 g and the magnesium is 12.0 g.
So mass of oxygen = 19.9 g − 12.0 g.

Feedback per option

  • A The magnesium oxide, 19.9 g, comes first; the magnesium, 12.0 g, is taken away from it.
  • B Mass of magnesium oxide, 19.9 g, minus mass of magnesium, 12.0 g.
  • C The masses are subtracted here, not added.
Q6scaffold

Calculate. What mass of oxygen joined the magnesium, in g?

Typed answer

Answer

Accepted: 7.9 g · 7.9 · 7.9 grams · 7.9g

mass of oxygen = 19.9 g − 12.0 g.
19.9 − 12.0 = 7.9.
So 7.9 g of oxygen joined the magnesium.
Q7bare

In a sealed container, 14.0 g of iron reacts with 8.0 g of sulfur, and every atom ends up in one product, iron sulfide. What is the mass of the iron sulfide, in g?

Typed answer

Answer

Accepted: 22.0 g · 22.0 · 22.0 grams · 22.0g · 22 g · 22 · 22 grams

mass of iron sulfide = mass of iron + mass of sulfur.
mass of iron sulfide = 14.0 g + 8.0 g.
14.0 + 8.0 = 22.0, so the iron sulfide has a mass of 22.0 g.
Q8bare

25.2 g of baking soda is heated in a lidded jar. It makes 15.9 g of a white powder, 2.7 g of water and some carbon dioxide. What is the mass of the carbon dioxide, in g?

Typed answer

Answer

Accepted: 6.6 g · 6.6 · 6.6 grams · 6.6g

mass of powder + mass of water + mass of carbon dioxide = mass of baking soda.
mass of carbon dioxide = 25.2 g − 15.9 g − 2.7 g.
25.2 − 15.9 − 2.7 = 6.6, so the carbon dioxide has a mass of 6.6 g.
Q9recall

A gas rises out of an open cup and drifts across the room. Does the gas that left have mass?

  1. A yes
  2. B no
Answer

Key: A — yes

A gas is matter.
Matter has mass.
So the gas that left the cup has mass, and it took that mass with it.

Feedback per option

  • A A gas is matter, so it has mass wherever it goes.
  • B Leaving the cup does not take the mass away from the gas: a gas is matter, with mass, in the cup or in the room.
Q10what

Suppose a fizzing tablet is dropped into water in an open cup on a balance. The tablet fizzes until it is gone. Compared with the first reading, what does the balance read at the end?

  1. A more than the first reading
  2. B the same as the first reading
  3. C less than the first reading
Answer

Key: C — less than the first reading

The fizz makes a gas, and a gas has mass.
The cup is open, so the gas floats away into the room.
The balance reads only what is left, so it reads less.

Feedback per option

  • A Nothing came in from the air here; a gas left, so the reading cannot rise.
  • B The cup is open, so the gas from the fizz floated away and took its mass with it.
  • C The fizz made a gas, the cup has no lid, and the gas floated away with its mass.
Q11why

The balance was zeroed with the empty open dish, and a heap of white powder reads 12.0 g. The powder is heated, a gas comes off, and the powder left reads 9.8 g. Explain what happened to the missing 2.2 g.

12.0 gbefore9.8 gafter

Starter: No mass was destroyed…

Answer

Model answer · ['no mass was destroyed', 'the gas is matter with mass, and the open dish let it float away', 'the balance reads only what is left, so the missing 2.2 g is the gas that left'] points

No mass was destroyed.
The powder gave off a gas, and a gas is matter with mass.
The dish is open, so the gas floated away into the air.
The balance reads only what is left in the dish.
So the missing 2.2 g is the mass of the gas that left.
Q12misconception

Jorge says: "When limestone is heated in an open dish, the 4.4 g that the balance loses is destroyed." Is Jorge correct?

  1. A yes
  2. B no
Answer

Key: B — no

The 4.4 g is the carbon dioxide made in the reaction.
The dish is open, so the gas floated away into the air with its mass.
In a lidded jar the balance would still read 10.0 g, so nothing was destroyed and Jorge is not correct.

Feedback per option

  • A Nothing was destroyed: the 4.4 g is carbon dioxide gas that floated out of the open dish; in a lidded jar the balance would still read 10.0 g.
  • B The 4.4 g floated out of the open dish as carbon dioxide gas, with its mass; in a lidded jar the balance would still read 10.0 g.
Q13transfer

A candle burns on a balance for an hour, and the reading falls. Where did the wax's atoms go?

  1. A the flame destroyed them, so they are gone
  2. B they turned into the heat and light of the flame
  3. C they left as carbon dioxide gas and water vapor
Answer

Key: C — they left as carbon dioxide gas and water vapor

Candle wax + oxygen → carbon dioxide + water.
Both products are gases here, and the candle is in the open.
So the wax's atoms floated away in the carbon dioxide and the water vapor.

Feedback per option

  • A No atom is destroyed; the atoms left in the gases the flame gave off.
  • B Heat and light are not atoms; the atoms left in the gases the flame gave off.
  • C Wax and oxygen react to make carbon dioxide and water vapor, and the open air lets those gases float away.
Your note · lesson 6: Work out a missing mass, and the open-dish trap
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 7 of 8Author: could do without a video187 words · about 1:34

Count the atoms on both sides

MAT-070 · Verify conservation of mass in a chemical equation — Confirm that a given balanced equation conserves mass by counting atoms on each side.

Script
SayScreen
Here is hydrogen burning, written with formulas: 2H₂ plus O₂ react to make 2H₂O.[the word strip; the formula form under it]
No atom is made or lost, so the left should match the right: do they?[question mark between the two sides]
Yes, they do, and counting shows it.[tick fades in between the two sides]
A coefficient counts whole particles and multiplies every count in the formula.[the 2 in 2H₂ boxed; two particles appear]
One: count each element on the left: 2H₂ is 4 hydrogen atoms, and O₂ is 2 oxygen atoms.[a row of 4 small dark circles; a row of 2 large open circles]
Two: count each element on the right: 2H₂O is 4 hydrogen atoms and 2 oxygen atoms.[matching rows appear under the right side]
Three: compare, kind for kind: 4 and 4, 2 and 2, so the equation obeys the law.[the table fills: yes, yes]
Now consider methane burning: carbon 1 and 1, hydrogen 4 and 4, oxygen 4 and 4, so it is a match.[the methane strip; key chip: gray circle = carbon atom; the table fills]
Suppose someone writes 2H₂ plus O₂ react to make H₂O: that puts 4 hydrogen atoms on the left and only 2 on the right.[the wrong line; the table: 4 against 2, 2 against 1; cross]
Atoms would have to vanish, so that line was written wrong.[label: written wrong]
So, an equation obeys the law of conservation of mass when each kind of atom counts the same on the left and on the right.[the rule slide: the hydrogen count table, 4 and 4, 2 and 2; nothing else printed]
Okay, now your turn.[closing screen: one line — "An equation obeys the law of conservation of mass when each kind of atom counts the same on the left and on the right."]

“Okay, now your turn.” — the attached question

video

Count the hydrogen atoms on each side of 2H₂ + O₂ → 2H₂O. How many are on each side?

  1. A 2 atoms
  2. B 4 atoms
  3. C 6 atoms
Answer

Key: B — 4 atoms

On the left, 2H₂ is two particles of 2 hydrogen atoms: 4.
On the right, 2H₂O is two particles of 2 hydrogen atoms: 4.
So there are 4 hydrogen atoms on each side.

Feedback per option

  • A 2 is the hydrogen count in ONE particle; the coefficient 2 doubles it.
  • B 2H₂ is 2 × 2 = 4 hydrogen atoms, and 2H₂O is 2 × 2 = 4 hydrogen atoms.
  • C 6 is not a count on either side; each side holds 4 hydrogen atoms.

Quiz after the video — the mastery check, 13 items

Q1recall

How many hydrogen atoms does 3H₂O hold in all?

  1. A 2 atoms
  2. B 3 atoms
  3. C 6 atoms
Answer

Key: C — 6 atoms

One H₂O particle holds 2 hydrogen atoms.
The coefficient 3 means three particles, so multiply: 3 × 2 = 6.
So 3H₂O holds 6 hydrogen atoms in all.

Feedback per option

  • A 2 is the hydrogen count in ONE water particle; the coefficient 3 multiplies it.
  • B 3 is the number of particles, not the hydrogen atoms.
  • C Three particles of 2 hydrogen atoms each: 3 × 2 = 6 hydrogen atoms.
Q2recall

Which of these is true in every chemical reaction?

  1. A no atom is made and no atom is lost
  2. B some atoms are made to build the products
  3. C some atoms are lost as heat
Answer

Key: A — no atom is made and no atom is lost

In a reaction the atoms only swap partners.
Every atom that was there before is still there after.
So no atom is made and no atom is lost.

Feedback per option

  • A Every atom that was there before is still there after: that is why the total mass is conserved.
  • B The products are built from atoms that were in the reactants; none are made.
  • C Heat is not made of atoms; no atom is lost.
Q3scaffold

Carbon monoxide burns: carbon monoxide + oxygen → carbon dioxide, written 2CO + O₂ → 2CO₂. Count the carbon atoms on the left.

Typed answer

Answer

Accepted: 2 · two · 2 carbon atoms · 2 atoms

On the left, only 2CO holds carbon.
The coefficient 2 means two particles of 1 carbon atom each: 2 × 1 = 2.
So there are 2 carbon atoms on the left.
Q4scaffold

In 2CO + O₂ → 2CO₂, count the carbon atoms on the right.

Typed answer

Answer

Accepted: 2 · two · 2 carbon atoms · 2 atoms

On the right, 2CO₂ holds the carbon.
Two particles of 1 carbon atom each: 2 × 1 = 2.
So there are 2 carbon atoms on the right.
Q5scaffold

In 2CO + O₂ → 2CO₂, count the oxygen atoms on the left.

Typed answer

Answer

Accepted: 4 · four · 4 oxygen atoms · 4 atoms

2CO holds 2 × 1 = 2 oxygen atoms.
O₂ holds 2 oxygen atoms.
Add them: 2 + 2 = 4 oxygen atoms on the left.
Q6scaffold

In 2CO + O₂ → 2CO₂, count the oxygen atoms on the right.

Typed answer

Answer

Accepted: 4 · four · 4 oxygen atoms · 4 atoms

2CO₂ is two particles of 2 oxygen atoms each.
Multiply: 2 × 2 = 4.
So there are 4 oxygen atoms on the right.
Q7scaffold

Compare your counts for 2CO + O₂ → 2CO₂, kind for kind. Does the equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Carbon: 2 on the left and 2 on the right.
Oxygen: 4 on the left and 4 on the right.
The counts match, so the equation obeys the law.

Feedback per option

  • A Carbon 2 and 2, oxygen 4 and 4: every count matches, so the equation obeys the law.
  • B Compare your counts again: carbon 2 and 2, oxygen 4 and 4; every count matches, so the equation obeys the law.
Q8bare

Sodium burns in chlorine: 2Na + Cl₂ → 2NaCl. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Sodium: 2 on the left, 2 on the right in 2NaCl.
Chlorine: 2 on the left in Cl₂, 2 on the right in 2NaCl.
The counts match, so the equation obeys the law.

Feedback per option

  • A Sodium 2 and 2, chlorine 2 and 2: a match.
  • B Count again: sodium 2 and 2, chlorine 2 and 2; every count matches.
Q9bare

A student writes hydrogen burning in chlorine as H₂ + Cl₂ → HCl. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: B — no

Hydrogen: 2 on the left in H₂, but 1 on the right in HCl.
Chlorine: 2 on the left, but 1 on the right.
The counts do not match, so the equation was written wrong.

Feedback per option

  • A Hydrogen: 2 on the left but only 1 on the right; the counts do not match.
  • B Hydrogen 2 against 1, chlorine 2 against 1: the counts do not match, so the line was written wrong.
Q10bare

A student writes magnesium burning as 2Mg + O₂ → MgO. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: B — no

Magnesium: 2 on the left in 2Mg, but 1 on the right in MgO.
Oxygen: 2 on the left, but 1 on the right.
The counts do not match, so the equation was written wrong.

Feedback per option

  • A Magnesium: 2 on the left but only 1 on the right; the counts do not match.
  • B Magnesium 2 against 1, oxygen 2 against 1: the counts do not match, so the line was written wrong.
Q11bare

Ammonia is made from nitrogen and hydrogen: N₂ + 3H₂ → 2NH₃. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Nitrogen: 2 on the left in N₂, 2 on the right in 2NH₃.
Hydrogen: 3 × 2 = 6 on the left, 2 × 3 = 6 on the right.
The counts match, so the equation obeys the law.

Feedback per option

  • A Nitrogen 2 and 2, hydrogen 3 × 2 = 6 and 2 × 3 = 6: a match.
  • B Count again: nitrogen 2 and 2; hydrogen 3 × 2 = 6 on the left and 2 × 3 = 6 on the right; every count matches.
Q12bare

Zinc and sulfur are heated together: Zn + S → ZnS. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Zinc: 1 on the left, 1 on the right.
Sulfur: 1 on the left, 1 on the right.
The counts match, so the equation obeys the law.

Feedback per option

  • A Zinc 1 and 1, sulfur 1 and 1: a match.
  • B Count again: zinc 1 and 1, sulfur 1 and 1; every count matches.
Q13misconception

Kavya says: "2H₂ + O₂ → H₂O obeys the law of conservation of mass, because both sides have hydrogen and oxygen." Is Kavya correct?

  1. A yes
  2. B no
Answer

Key: B — no

The law is about the count of each kind of atom, not only which kinds appear.
Hydrogen: 4 on the left, 2 on the right. Oxygen: 2 on the left, 1 on the right.
The counts do not match, so Kavya is not correct.

Feedback per option

  • A Kavya's reason is not the test: having the same elements is not enough; the counts must match, and hydrogen is 4 against 2, oxygen 2 against 1.
  • B The counts must match kind for kind: hydrogen is 4 against 2 and oxygen 2 against 1, so the line was written wrong and Kavya is not correct.
Your note · lesson 7: Count the atoms on both sides
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 8 of 8Author: definitely a video197 words · about 1:38

Photosynthesis: a tree's mass comes from the air

MAT-072 · Photosynthesis as a conservation-of-mass example — Show that atoms are conserved in the photosynthesis equation by counting atoms on each side.

Script
SayScreen
About 400 years ago, a scientist planted a small willow tree of 2.3 kilograms in a tub of soil.[a small tree in a tub; label 2.3 kg]
He only watered it; five years on, the tree was 76.7 kilograms and the soil had lost 0.06 kilograms.[the tree grows tall; the soil line stays; labels 76.7 kg and 0.06 kg]
Where did the other 74 kilograms of tree come from?[question mark over the tree]
It came from the air and the water.[arrows from the air and the watering can to the tree]
Plants build glucose from carbon dioxide and water, using light: this reaction is called photosynthesis.[strip: carbon dioxide + water → glucose + oxygen; a sun above; carbon dioxide molecules flow in from the air and water molecules up from the can]
With formulas, it reads: 6CO₂ plus 6H₂O react to make C₆H₁₂O₆ plus 6O₂.[the formula form under the strip]
Count carbon: 6 and 6; hydrogen: 12 and 12; oxygen: 18 and 18.[rows of circles each side; key chip: gray circle = carbon atom, small dark = hydrogen atom, large open = oxygen atom; the table: yes, yes, yes]
Every count matches, so the equation obeys the law of conservation of mass.[chip: A MATCH]
Only carbon dioxide brings carbon, so every carbon atom in the glucose came from the air.[the gray circles trace back to the carbon dioxide]
Only water brings hydrogen, so every hydrogen atom came from the watering can.[the small dark circles trace back to the water]
The tree builds its leaves, wood and roots from the glucose.[the tree thickens as glucose flows into it]
Plants build glucose from carbon dioxide and water.[the rule slide: the two tubs with the photosynthesis strip above them; nothing else printed]
So a tree's new mass comes from the air and the water, not the soil.[the arrows from the air and the can glow; the soil line unchanged]
So the willow's extra 74 kilograms is air and water, built into a tree.[the tall tree; the soil line unchanged]
Okay, now your turn.[closing screen: bullets — • Plants build glucose from carbon dioxide and water • A tree's new mass comes from the air and the water, not the soil]

“Okay, now your turn.” — the attached question

video

A willow grows from 2.3 kg to 76.7 kg while its tub of soil barely changes. Where does the new mass come from?

  1. A the soil
  2. B the air and the water
  3. C the sunlight, which turns into wood
Answer

Key: B — the air and the water

Plants build glucose from carbon dioxide and water.
The tree builds its wood from that glucose.
So the new mass comes from the air and the water, not the soil.

Feedback per option

  • A The soil loses only 0.06 kg, so it supplies almost none of the new mass.
  • B The plant builds glucose from carbon dioxide in the air and water from the can, then builds wood from the glucose.
  • C Light is needed, but light is not made of atoms; the atoms come from the air and the water.

Quiz after the video — the mastery check, 14 items

Q1recall

Which two substances does a plant use to build glucose in photosynthesis?

  1. A water and minerals from the soil
  2. B oxygen from the air and soil
  3. C carbon dioxide and water
Answer

Key: C — carbon dioxide and water

Plants build a sugar called glucose from carbon dioxide and water.
Light is needed, but light is not made of atoms.
So the two reactants are carbon dioxide and water.

Feedback per option

  • A Soil is not a reactant; the plant builds glucose from carbon dioxide and water.
  • B Oxygen is a product of photosynthesis, and soil is not a reactant.
  • C Plants build glucose from carbon dioxide and water, using light.
Q2recall

To check that an equation obeys the law of conservation of mass, what do you compare?

  1. A the count of each kind of atom on each side
  2. B the number of particles on each side of the arrow
  3. C the number of formulas on each side
Answer

Key: A — the count of each kind of atom on each side

The law says no atom is made and no atom is lost.
So each kind of atom must count the same on the left and on the right.
That is what you compare.

Feedback per option

  • A An equation obeys the law when each kind of atom counts the same on both sides.
  • B The number of particles can change; it is the atoms of each kind that must match.
  • C How many formulas there are does not matter; the atoms of each kind must match.
Q3scaffold

Living things use glucose in a reaction that runs the other way: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. Count the carbon atoms on the left.

Typed answer

Answer

Accepted: 6 · six · 6 carbon atoms · 6 atoms

Only C₆H₁₂O₆ holds carbon on the left.
The small low number after the C is 6.
So there are 6 carbon atoms on the left.
Q4scaffold

In C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, count the carbon atoms on the right.

Typed answer

Answer

Accepted: 6 · six · 6 carbon atoms · 6 atoms

Only 6CO₂ holds carbon on the right.
Six particles of 1 carbon atom each: 6 × 1 = 6.
So there are 6 carbon atoms on the right.
Q5scaffold

In C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, count the hydrogen atoms on the left.

Typed answer

Answer

Accepted: 12 · twelve · 12 hydrogen atoms · 12 atoms

Only C₆H₁₂O₆ holds hydrogen on the left.
The small low number after the H is 12.
So there are 12 hydrogen atoms on the left.
Q6scaffold

In C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, count the hydrogen atoms on the right.

Typed answer

Answer

Accepted: 12 · twelve · 12 hydrogen atoms · 12 atoms

Only 6H₂O holds hydrogen on the right.
Six particles of 2 hydrogen atoms each: 6 × 2 = 12.
So there are 12 hydrogen atoms on the right.
Q7scaffold

In C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, count the oxygen atoms on the left. Add the oxygen in C₆H₁₂O₆ to the oxygen in 6O₂.

Typed answer

Answer

Accepted: 18 · eighteen · 18 oxygen atoms · 18 atoms

C₆H₁₂O₆ holds 6 oxygen atoms.
6O₂ holds 6 × 2 = 12 oxygen atoms.
Add them: 6 + 12 = 18 oxygen atoms on the left.
Q8scaffold

In C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, count the oxygen atoms on the right. Add the oxygen in 6CO₂ to the oxygen in 6H₂O.

Typed answer

Answer

Accepted: 18 · eighteen · 18 oxygen atoms · 18 atoms

6CO₂ holds 6 × 2 = 12 oxygen atoms.
6H₂O holds 6 × 1 = 6 oxygen atoms.
Add them: 12 + 6 = 18 oxygen atoms on the right.
Q9scaffold

Compare your counts for C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, kind for kind. Does the equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Carbon: 6 and 6. Hydrogen: 12 and 12. Oxygen: 18 and 18.
Each kind of atom counts the same on both sides.
So the equation obeys the law.

Feedback per option

  • A Carbon 6 and 6, hydrogen 12 and 12, oxygen 18 and 18: every count matches.
  • B Compare your counts again: carbon 6 and 6, hydrogen 12 and 12, oxygen 18 and 18; every count matches, so the equation obeys the law.
Q10bare

Photosynthesis is written 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: A — yes

Carbon: 6 on the left in 6CO₂, 6 on the right in C₆H₁₂O₆.
Hydrogen: 12 and 12. Oxygen: 12 + 6 = 18 on the left, 6 + 12 = 18 on the right.
The counts match, so the equation obeys the law.

Feedback per option

  • A Carbon 6 and 6, hydrogen 12 and 12, oxygen 12 + 6 = 18 and 6 + 12 = 18: every count matches.
  • B Count again: carbon 6 and 6, hydrogen 12 and 12, oxygen 18 and 18; every count matches.
Q11bare

A student writes photosynthesis as 6CO₂ + 6H₂O → C₆H₁₂O₆ + O₂. Does this equation obey the law of conservation of mass?

  1. A yes
  2. B no
Answer

Key: B — no

Oxygen on the left: 12 + 6 = 18.
Oxygen on the right: 6 in C₆H₁₂O₆ + 2 in O₂ = 8.
The counts do not match, so the equation was written wrong.

Feedback per option

  • A Oxygen: 18 on the left, but only 6 + 2 = 8 on the right; the counts do not match.
  • B Oxygen 18 against 8: the counts do not match, so the line was written wrong.
Q12misconception

A willow grown in a tub for five years gained 74 kg, and its soil lost only 0.06 kg. Lachlan says: "The willow's extra 74 kg came from the soil, because that is what the roots sit in." Is Lachlan correct?

  1. A yes
  2. B no
Answer

Key: B — no

The soil lost only 0.06 kg in five years, far less than 74 kg.
The plant builds glucose from carbon dioxide and water.
So the new mass came from the air and the water, and Lachlan is not correct.

Feedback per option

  • A The soil cannot be the source: it lost only 0.06 kg. The plant built its glucose from carbon dioxide in the air and water from the can.
  • B The soil lost only 0.06 kg, far less than 74 kg; the plant built its glucose from carbon dioxide in the air and water from the can.
Q13misconception

Meike says: "Every carbon atom in the glucose came from carbon dioxide, because carbon dioxide is the only reactant with carbon." Is Meike correct?

  1. A yes
  2. B no
Answer

Key: A — yes

The atoms in a new substance come from the substances that were there before.
Of the two reactants, only carbon dioxide holds carbon atoms.
So every carbon atom in the glucose came from carbon dioxide, and Meike is correct.

Feedback per option

  • A The atoms in a new substance come from the substances that were there before, and only carbon dioxide brought carbon.
  • B Meike is right: the atoms in a new substance come from the substances that were there before, and of the two reactants only carbon dioxide brought carbon.
Q14transfer

A corn plant grows in a large pot for a summer and gains 2.0 kg. The soil in the pot is weighed at the start and at the end. What does the soil's mass do?

  1. A it falls by about 2.0 kg
  2. B it barely changes
  3. C it rises by about 2.0 kg
Answer

Key: B — it barely changes

Plants build glucose from carbon dioxide and water.
The plant's new mass is built from that glucose, so almost none of it comes from the soil.
So the soil's mass barely changes.

Feedback per option

  • A The plant did not take its new mass from the soil; the soil supplies almost none of it.
  • B The corn built its mass from carbon dioxide in the air and from water, so the soil's mass barely changes.
  • C Nothing adds mass to the soil; the plant's new atoms came from the air and the water.
Your note · lesson 8: Photosynthesis: a tree's mass comes from the air
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Summary video · everything taught, in order, just before the PP100260 words · about 2:10

Summary: Chemical reactions and conservation of mass

Script, part 1 (133 words)
SayScreen
Here is everything we found out about chemical reactions and conservation of mass.[a still: the rust pair, the methane strip and the lidded jar]
The atoms in a new substance come from the substances that were there before.[the rust pair: 4 and 4 under each box]
In a chemical reaction the atoms let go of their old partners and join new ones. So new substances form.[the hydrogen pair; chip: CHEMICAL REACTION]
Melting and dissolving move the particles around without changing them. So they are not chemical reactions.[the ice pair and the sugar pair; crosses]
The substances that go into a reaction are called the reactants, and the substances that come out are called the products.[the labeled methane strip; chips: REACTANTS, PRODUCTS]
A word equation writes the reactants on the left, an arrow that reads “react to make”, and the products on the right.[the strip; chip: REACT TO MAKE]
And to find every element in a reaction, read each symbol, look it up on the periodic table, and write each element once.[the formula form with symbols underlined; the periodic table]
Okay, now your turn.[closing screen: bullets — • The atoms in a new substance come from the substances that were there before • In a chemical reaction the atoms let go of their old partners and join new ones • Reactants → products: the arrow means “react to make” • Read each symbol to find the elements]

“Okay, now your turn.” — the check question between the parts

video

Iron and oxygen react to make iron oxide. Which substances are the reactants?

  1. A iron and oxygen
  2. B iron oxide
  3. C iron oxide and oxygen
Answer

Key: A — iron and oxygen

The substances that go into a reaction are called the reactants.
Iron and oxygen go in.
So iron and oxygen are the reactants.

Feedback per option

  • A The substances that go into a reaction are the reactants: iron and oxygen.
  • B Iron oxide comes out of the reaction, so it is the product.
  • C Iron oxide is the product; the reactants are iron and oxygen.
Script, part 2 (127 words)
SayScreen
Here is everything we found out about mass in a chemical reaction.[a still: the lidded jar at 250.0 g]
The total mass of the products equals the total mass of the reactants: this is the law of conservation of mass.[the lidded jar: 250.0 g and 250.0 g; chip: LAW OF CONSERVATION OF MASS]
To find a missing mass, write the law in the reaction's own substances, make the unknown the subject, substitute, and calculate.[a card: mass of calcium oxide + mass of carbon dioxide = mass of calcium carbonate; no numbers]
In an open container a gas made by the reaction floats away, so the balance reads less. No mass was destroyed.[the open dish beside its readout 5.6 g; chip: NOTHING DESTROYED]
An equation obeys the law of conservation of mass when each kind of atom counts the same on the left and on the right.[the hydrogen count table: 4 and 4, 2 and 2]
And plants build glucose from carbon dioxide and water. So a tree's new mass comes from the air and the water, not the soil.[the two tubs; the photosynthesis strip]
Okay, now your turn.[closing screen: bullets — • Total mass of the products = total mass of the reactants • A gas that floats away is not destroyed • Each kind of atom counts the same on both sides • A tree's new mass comes from the air and the water]

“Okay, now your turn.” — the two questions after part 2

video

Limestone is heated in an open dish, and the balance reading falls by 4.4 g. What happens to the missing 4.4 g?

  1. A it is destroyed by the heat
  2. B it soaks into the dish's walls
  3. C it leaves as carbon dioxide gas
Answer

Key: C — it leaves as carbon dioxide gas

The reaction makes 4.4 g of carbon dioxide gas.
The dish is open, so the gas floats away into the air.
So the missing 4.4 g leaves as carbon dioxide gas.

Feedback per option

  • A No mass is destroyed in a reaction; the gas floats away.
  • B Nothing soaks in; the carbon dioxide gas floats out of the open dish.
  • C The reaction makes carbon dioxide gas, and the open dish lets it float away with its mass.
video

An equation is written as 2H₂ + O₂ → 2H₂O. Does it obey the law of conservation of mass?

  1. A Yes: 4 hydrogen atoms and 2 oxygen atoms on each side.
  2. B No: the left side has more atoms than the right.
Answer

Key: A — Yes: 4 hydrogen atoms and 2 oxygen atoms on each side.

An equation obeys the law of conservation of mass when each kind of atom counts the same on both sides.
Hydrogen is 4 and 4; oxygen is 2 and 2.
So the equation obeys the law.

Feedback per option

  • A Each kind of atom counts the same on both sides, so the equation obeys the law.
  • B Count again: 2H₂ is 4 hydrogen atoms and O₂ is 2 oxygen atoms; 2H₂O is 4 hydrogen atoms and 2 oxygen atoms. The counts match.
Your note · the summary video
What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

  • Clear and concise language
  • Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
  • No "clangers" (content that causes a problematic misconception)
  • Appropriate questions
  • Initial testing
  • Expansion into harder questions (no exam)
  • The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Applied without asking

Rulings you have already given; in force on every card above, not re-asked.

The topic’s fixed wording (the lexicon the scripts repeat)
  • The atoms in a new substance come from the substances that were there before.
  • In a chemical reaction the atoms let go of their old partners and join new ones. So new substances form.
  • Melting and dissolving move the particles around without changing them. So they are not chemical reactions.
  • The substances that go into a reaction are called the reactants, and the substances that come out are called the products.
  • A word equation writes the reactants on the left, an arrow that reads “react to make”, and the products on the right.
  • To find every element in a reaction, read each symbol, look it up on the periodic table, and write each element once.
  • The total mass of the products equals the total mass of the reactants: this is the law of conservation of mass.
  • To find a missing mass, write the law in the reaction's own substances, make the unknown the subject, substitute, and calculate.
  • In an open container a gas made by the reaction floats away, so the balance reads less. No mass was destroyed.
  • An equation obeys the law of conservation of mass when each kind of atom counts the same on the left and on the right.
  • Plants build glucose from carbon dioxide and water. So a tree's new mass comes from the air and the water, not the soil.

Scripts, questions and quizzes are read from the course content as it stands today; the student site for this topic is here.