Changes you can undo and changes you can't
Tests: 4 of 10 right · Exam: 3 of 4 right · Kind: ★ · Understood: 8 of 14 · Run: 2026-10-18, commit f3c23ea72
Lesson 9 of the chemistry course of Mova's primary school, as Mova's small model took its tests: it had read this lesson and the ones before it and learned from their exercises. Each test shows the options in the order the student saw them, its choice, the right answer, the score of every option and why it chose. The lesson itself, sentence by sentence with trees and pragmatics: the lesson in the corpora.
Every question of this lesson and each of its options parsed by Mova, with trees and pragmatics: the lesson's questions in the corpora.
Test 1 · ★ · wrong ✗
Your friend says: "Bubbles mean a new substance, so boiling water is a chemical change." Put him right.
- 1. Boiling makes hydrogen and oxygen — no support
- 2. The bubbles are air from the kettle — no support
- 3. He is right, boiling breaks the old water up and makes brand new water from it — ← Mova's choice · score 6
- 4. The bubbles are water vapour, still water, so it is reversible — ✓ the right answer · no support
Why: It took the question to ask which statement is true. It chose option 3 with score 6, the only option with support. Its support: lesson 9, line 8: «Burning paper makes new substances (carbon dioxide, water vapour and ash) by joining the paper's atoms with oxygen; the atoms are not destroyed.», reached through the remembered sentence the question matched. What matched: the same action «make» (+4); the same thing acted on «new substances» (+4). Against it: a different doer (counts against) (-2). The right option, 4, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics
Test 2 · ★ · wrong ✗
"if atoms never get destroyed, why can't I glue my burnt homework back together?" Best answer?
- 1. The paper is hiding in the smoke — no support
- 2. The atoms are now in new substances in the air and ash — ✓ the right answer · no support
- 3. You can, with strong enough glue — no support
- 4. The atoms were all destroyed by the fire, so there is nothing left to glue — ← Mova's choice · score 0
Why: It took the question to ask why something happens (its cause). It chose option 4 with score 0, the only option with support. Its support: lesson 9, line 8: «Burning paper makes new substances (carbon dioxide, water vapour and ash) by joining the paper's atoms with oxygen; the atoms are not destroyed.», reached through the option's own match among the sentences about the question's things. What matched: the same action «destroy» (+2); the same thing acted on «atoms» (+2). Against it: one says «not», the other does not (counts against) (-4). The right option, 2, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics
Test 3 · ★ · right ✓
What would happen if you opened the oven far too early while a cake was rising?
- 1. Nothing at all would change — no support
- 2. It would rise twice as fast, because the cool air from the kitchen helps it grow — score 3
- 3. It would turn back into batter at once — no support
- 4. It could sink, as bubbles collapse before the walls are firm — ← Mova's choice · ✓ the right answer · score 4
Why: It took the question to ask what happens next. It chose option 4 with score 4, against 3 for the next best. Its support: lesson 9, line 10: «Baking a cake sets proteins, makes gas bubbles that make it rise, and browns sugars; a cake taken out too early can sink.», reached through the same lesson line as the sentence the question matched. What matched: the same action «sink» (+2); the same doer «cake» (+2). · the question and its options parsed, with trees and pragmatics
Test 4 · ★ · right ✓
A cartoon chef "un-fries" an egg by putting it in the fridge. What is wrong?
- 1. Cooling cannot undo a cooked egg — ← Mova's choice · ✓ the right answer · no support
- 2. It would only work in a very cold freezer — no support
- 3. The cold egg would turn into a chick — no support
- 4. Nothing, eggs uncook when they get cold — no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Test 5 · ★ · wrong ✗
Your sister says: "A colour change always means a chemical change." Is that right?
- 1. Yes, but only for red — no support
- 2. No, colour never changes in chemistry — no support
- 3. Yes, every colour change is chemical, even mixing paints — ← Mova's choice · score 3
- 4. No, mixing paints changes colour without new substances — ✓ the right answer · no support
Why: It took the question to ask which statement is true. It chose option 3 with score 3, the only option with support. Its support: lesson 9, line 17: «A clue alone can mislead: boiling water bubbles but no new substance forms, and a colour change can also be just paint or mixing.», reached through the option's own match among the sentences about the question's things. What matched: the same thing acted on «paint» (+2); the same doer «colour change» (+1). The right option, 4, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics
Test 6 · ★ · wrong ✗
Why do archaeologists find so many broken pots?
- 1. Ancient people broke all of their old pots on purpose every year, for good luck — ← Mova's choice · no support
- 2. Fired pottery does not rot or dissolve, so it lasts thousands of years — ✓ the right answer · no support
- 3. Clay always turns into pots in soil — no support
- 4. Pots grow in the ground — no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Test 7 · ★ · right ✓
"can't I just scrape off the burnt bits and get my bread back?" Best answer?
- 1. The toasted layer is new substances, the bread can't come back — ← Mova's choice · ✓ the right answer · no support
- 2. Yes, scraping off the brown layer turns it straight back into soft bread — no support
- 3. Yes, if you add water — no support
- 4. Only for white bread — no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Test 8 · ★ · wrong ✗
Grandma's chocolate bar looks pale and grey. Your brother says it's poison. What is the truth?
- 1. He is right, the whole cupboard of food must be thrown away — ← Mova's choice · no support
- 2. It is chalk added by the shop — no support
- 3. It is mould that glows — no support
- 4. It is fat bloom from melting and setting, still safe — ✓ the right answer · no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Test 9 · ★ · wrong ✗
Which of these is a change you can undo?
- 1. Bread being toasted — ← Mova's choice · no support
- 2. Water vapour cooling back into liquid water — ✓ the right answer · no support
- 3. A firework exploding in the sky — no support
- 4. Paper burning to ash — no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Test 10 · ★ · right ✓
Is boiling water a reversible change?
- 1. No, steam is a totally new substance — no support
- 2. Yes, steam condenses back to water — ← Mova's choice · ✓ the right answer · score 4
- 3. Only high up on a tall mountain top — no support
- 4. No, boiling destroys the water for good, so it is gone — no support
Why: It took the question to ask which statement is true. It chose option 2 with score 4, the only option with support. Its support: lesson 4, line 15: «Steam can burn worse than boiling water, because it gives out extra heat as it turns back into water.», reached through the same lesson line as the sentence the question matched. What matched: the same circumstance (+3); the same doer «steam» (+2). Against it: a different action (counts against) (-1). · the question and its options parsed, with trees and pragmatics
Exam question 1 · formal language · right ✓
Which of the following statements most accurately characterises a reversible change?
- 1. A change accompanied invariably by the emission of light — no support
- 2. A change in which atoms are destroyed — no support
- 3. A change in which new substances are formed by the rearrangement of atoms within molecules — no support
- 4. A change in which no new substance is formed and the original may be recovered — ← Mova's choice · ✓ the right answer · score 10
Why: It took the question to ask who or what does it. It chose option 4 with score 10, the only option with support. Its support: lesson 9, line 11: «Folding, bending and cutting change only shape; they are physical changes, not chemical ones.», reached through the remembered sentence the question matched. What matched: it fills the role the question asks for (+6); the same doer «proteins» (+4). · the question and its options parsed, with trees and pragmatics
Exam question 2 · formal language · wrong ✗
Identify the principal reason for which the frying of an egg cannot be reversed in the kitchen.
- 1. The egg has been frozen solid — ← Mova's choice · no support
- 2. The yolk has been converted to metal — no support
- 3. The egg has lost its entire mass to the surrounding air — no support
- 4. The proteins have unfolded and become permanently entangled — ✓ the right answer · no support
Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics
Exam question 3 · formal language · right ✓
Select the response that is consistent with the established facts concerning the combustion of paper.
- 1. The paper may be restored by cooling the ash — no support
- 2. New substances are produced, the atoms of the paper being combined with oxygen — ← Mova's choice · ✓ the right answer · score 8
- 3. The atoms of the paper are wholly annihilated by the heat of the flame and cease to exist — no support
- 4. The paper is converted into pure water — no support
Why: It took the question to ask which statement is true. It chose option 2 with score 8, the only option with support. Its support: lesson 9, line 8: «Burning paper makes new substances (carbon dioxide, water vapour and ash) by joining the paper's atoms with oxygen; the atoms are not destroyed.», reached through the remembered sentence the question matched. What matched: the same action «make» (+4); the same thing acted on «new substances» (+4). · the question and its options parsed, with trees and pragmatics
Exam question 4 · formal language · right ✓
It is given that bubbles are observed in a liquid. Determine whether this observation alone establishes that a chemical change has occurred.
- 1. It does, provided the liquid is water — no support
- 2. It does, in all cases without exception, bubbles being proof of a new substance — score 3
- 3. It does not, since boiling water bubbles without forming a new substance — ← Mova's choice · ✓ the right answer · score 6
- 4. It does, provided the vessel is metal — no support
Why: It took the question to ask which statement is true. It chose option 3 with score 6, against 3 for the next best. Its support: lesson 9, line 5: «The clues can trick you, though: boiling water bubbles, yet it is still water.», reached through the remembered sentence the question matched. What matched: the same action «boil» (+4); the same thing acted on «water bubbles» (+4). Against it: a different doer (counts against) (-2). · the question and its options parsed, with trees and pragmatics
This page in Markdown → https://md.mova.elamur.ai/free/en/school-run/chemistry/9-changes-you-can-and-cannot-undo/