Angela's Tools · Chapter 13 · Atoms in Chemical Reactions Worksheet 8 of 10

Where Did the Mass Go? A Twelve-Card Evidence Sort

Learning target: I can work with a group to sort balance-reading evidence from twelve changes into cases where mass left, joined or stayed, explain each case with atoms crossing or not crossing a boundary, and write one rule that fits every card.

Collaborative investigationAbout 50 minSmall group MS-PS1-5 · practice collaborationdiscussiondata analysis
NameDatePeriod

Directions

Work in groups of three or four. Step 1 (alone, 5 minutes): before touching the cards, answer Part A. Step 2 (group, 25 minutes): spread out the twelve cards, follow the group steps, and fill in the group record. Card 12 is a challenge card; sort the other eleven first. Step 3 (challenge, 10 minutes): swap your one-sentence rule with a neighboring group and test their rule against your hardest card. Step 4 (alone, 10 minutes): answer Part C by yourself. All readings on the cards are teaching values, written to be realistic; none were measured in this classroom.

You will need: Twelve cards per group, cut from the card sheet, Sticky notes for O and C labels, Group record table, Pencils

Twelve evidence cards (teaching values; cut apart before class)
1 Card 1: Fizzing tablets in an open glassA glass of water on a balance reads 231.60 g with two fizzing antacid tablets resting on the rim. The tablets are dropped in. They fizz for two minutes and disappear. Final reading: 230.40 g.
2 Card 2: Fizzing tablet in a capped bottleThe same kind of tablet is dropped into a rigid plastic bottle of water, and the cap is screwed on at once. Reading before: 238.20 g. The bottle fizzes and feels firm. Reading after two minutes: 238.20 g.
3 Card 3: Nail left out in the rainA clean iron nail reads 5.40 g. It is left outdoors for a rainy week, then dried. It is covered with orange-brown flakes and reads 5.47 g.
4 Card 4: Candle burning in open airA candle in a dish reads 48.20 g. It burns for ten minutes in the open. A cold glass held above the flame fogs with water droplets. Reading after: 46.60 g.
5 Card 5: Ice melting in a sealed bagAn ice cube sealed in a zip bag reads 24.80 g. An hour later it has completely melted. Reading: 24.80 g.
6 Card 6: Copper pad on a hot plateA shiny copper scouring pad reads 2.40 g. It is heated on a hot plate for ten minutes in open air, turns black, and cools. Reading: 2.58 g.
7 Card 7: Sugar stirred into teaA mug of warm tea reads 310.50 g, and a spoon of sugar beside it reads 4.00 g. The sugar is stirred into the open mug until it disappears. Reading of mug and tea: 314.50 g.
8 Card 8: Glow stick snapped in its tubeA sealed glow stick reads 18.30 g. It is snapped and glows brightly for an hour, then fades. Reading: 18.30 g.
9 Card 9: Match burned to ashA wooden match reads 0.12 g. It is struck and burns completely in open air, leaving a black, curled stick. Reading: 0.03 g.
10 Card 10: Bread dough risingA bowl of yeast dough, loosely covered with a cloth, reads 820.00 g. After an hour the dough has doubled in size and smells yeasty. Reading: 818.60 g.
11 Card 11: Magnesium ribbon burned (teacher demo)A strip of magnesium metal reads 0.24 g. The teacher burns it in open air behind a shield; it gives a blinding white light and leaves a white powder. The powder, collected carefully, reads 0.40 g.
12 Card 12 (challenge): Baking soda and vinegar in a sealed zip bagVinegar in a zip bag with a packet of baking soda reads 171.30 g. The bag is sealed, the packet is tipped into the vinegar, and the bag puffs up tight. Nothing leaks. Reading: 170.80 g. Hint: the puffed bag sits on the pan a little like a balloon would.

Part A: Predict alone (before sorting)

1.Read only the first sentence of Cards 3, 5 and 9 (not the readings). For each, predict whether the reading will go up, down or stay the same, and give a one-phrase reason. You will check these after the sort.

Part B: Group sort

  1. Sort Cards 1 to 11 into three piles by what the reading did: FELL, ROSE, or STAYED THE SAME. Write the change for each card with a sign and units.
  2. For each card, decide whether the system on the balance was open (matter could cross its boundary) or closed (nothing could cross). Mark each card O or C with a sticky note.
  3. For every FELL card, name what left and what it was made of. For every ROSE card, name what joined and where it came from. For every STAYED card, say why nothing crossed the boundary, and whether a reaction happened at all.
  4. Fill in the group record table. Then write one sentence, your group rule, that explains all eleven readings. It must mention atoms and a boundary.
  5. Now read Card 12. Test your rule against it. If the rule says the reading should not have changed, do not throw the rule out; look for a reason the balance might read low without any atoms leaving. Write your best explanation in q3.
  6. Swap rules with a neighboring group. Pick your hardest card and ask them to explain it with their rule. Record the strongest challenge you received and how you answered it.
Group record (fill in)
CardChange (g, with sign)Open or closed?What crossed the boundary (or nothing)Where those atoms are now
1
2
3
4
5
6
7
8
9
10
11
12
2.Group answer: Write your group rule in one sentence. Then list which cards go in each pile (FELL, ROSE, STAYED).
3.Group answer: Card 12 is sealed, yet the reading fell by 0.50 g. Does this break your rule? Explain what your group thinks is happening, using the hint on the card, and describe one change to the setup that would test your idea.

Part C: Individual accountability (complete alone)

4.Check your Part A predictions against the cards. Which were right? For any that were wrong, say what you now know that you did not know before.
5.Choose one FELL card and one ROSE card. For each, explain the reading with atoms: which atoms crossed the boundary, which direction, and what new substance they are part of now.
6.Cards 5 and 7 both STAYED, but Card 7 is an open mug. Explain why an open system can keep its mass, and say whether a chemical reaction happened on either card.
7.Pick Card 4, 9 or 10. Describe one change to the setup that would make its reading stay the same, and explain, using the atoms, why your change works. Then explain why that steady reading would still not mean the reaction had stopped.

Start with the boundary

If the sort feels hard, start by drawing an imaginary line around everything on the balance for each card and asking one question: could a gas get across this line? Sealed bottle, sealed bag, sealed tube: no. Open glass, open dish, cloth cover, open air: yes. Then ask whether the card describes a gas being made (fizzing, flame, yeast) or a gas from the air joining a solid (rust, black coating, white powder). Gas made and able to leave means FELL; gas from the air joining means ROSE; no gas crossing means STAYED. A change with no new substance (melting, dissolving) is not a reaction, but the atoms are still all there.

Two cards that look alike

Cards 3 and 6 both ROSE and both show a metal gaining mass from the air. A rusting nail needs both oxygen and water from its surroundings; the heated copper pad needs only oxygen. Design a pair of sealed experiments that could show whether water is needed for rust: describe what goes in each sealed container, what you would keep the same, what reading or appearance you would expect in each after a week, and why the sealed reading should be the same before and after in both containers no matter what happens to the nail.

Angela's Tools · Chapter 13 · Atoms in Chemical ReactionsWorksheet 8 of 10