Tarnish and how metals change

Tests: 5 of 10 right · Exam: 2 of 4 right · Kind: ★ · Understood: 9 of 14 · Run: 2026-10-18, commit f3c23ea72

Lesson 14 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 · ★ · right ✓

"my mate says cola dissolves a tooth overnight, legit?"

1. Yes, it's totally gone by morning, there's nothing left in the glass — no support
2. No, that's a myth, but sugary acid drinks harm teeth over time — ← Mova's choice · ✓ the right answer · score 8
3. Yes, but only diet cola does it — no support
4. No, cola has no acid in it at all — score 5

Why: It took the question to ask which statement is true. It chose option 2 with score 8, against 5 for the next best. Its support: lesson 14, line 16: «Cola has a weak acid that slowly loosens rust on a nail; the story that cola dissolves a tooth overnight is a myth, though sugary acid drinks do harm teeth ove…», reached through the same lesson line as the sentence the question matched. What matched: the same action «harm» (+3); the same doer «sugary acid drinks» (+2); the same thing acted on «teeth» (+2); the same property (+1). · the question and its options parsed, with trees and pragmatics

Test 2 · ★ · wrong ✗

Grandma's silver teapot is dark; Mia wants to scrub hard with polish every week. What's the catch?

1. Polish turns silver into copper — ← Mova's choice · no support
2. Polish makes the silver rust like iron — no support
3. Scrubbing makes the tarnish come back green — no support
4. Each polish rubs a little silver away — ✓ the right answer · no support

Why: Nothing it remembers matched the question, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Test 3 · ★ · wrong ✗

A statue of a dog in the park has a shiny nose but dark ears. Why?

1. People rub its nose for luck, wiping off the tarnish — ✓ the right answer · no support
2. Rain falls only on its ears — no support
3. Its nose was made of real gold from the very start — ← Mova's choice · score 5
4. Dogs in the park lick the ears dark — no support

Why: It took the question to ask why something happens (its cause). It chose option 3 with score 5, the only option with support. Its support: lesson 1, line 3: «Atoms and the particles they make are never still: they jiggle, bump and drift, which is why Mum's perfume reaches your nose from across the room without anybo…», reached through the option's own match among the sentences about the question's things. What matched: the same action «reach» (+3); the same thing acted on «nose» (+2). The right option, 1, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

Test 4 · ★ · right ✓

Jake: "gold's dead old on that frame but it's still shiny, someone must polish it". What's the truth?

1. Old gold always goes black eventually — no support
2. Gold doesn't tarnish, so it stays bright — ← Mova's choice · ✓ the right answer · score 7
3. The frame is plastic painted gold-coloured — no support
4. Gold is polished every week by museums — no support

Why: It took the question to ask what it is done to. It chose option 2 with score 7, the only option with support. Its support: lesson 14, line 15: «Gold almost never reacts with oxygen or sulphur, so it does not tarnish and is used on domes and picture frames.», reached through the remembered sentence the question matched. What matched: the same action «tarnish» (+4); the same doer «gold» (+3). · the question and its options parsed, with trees and pragmatics

Test 5 · ★ · right ✓

Your sister's new ring turns her finger green. She panics: "am I poisoned??"

1. No, it means she ate too many green vegetables — no support
2. Yes, go to hospital straight away — no support
3. No, it's copper reacting with sweat, harmless — ← Mova's choice · ✓ the right answer · score 3
4. Yes, green skin means blood poisoning — 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 14, line 10: «A cheap ring with copper in it can leave a harmless green mark on skin, because sweat with its salt and acid reacts with the copper; the mark simply washes off.», reached through a sentence linked to the one the question matched. What matched: the same action «react» (+2); the same circumstance (+2). Against it: a different doer (counts against) (-1). · the question and its options parsed, with trees and pragmatics

Test 6 · ★ · wrong ✗

If you stored silver forks in a box with rubber bands and boiled eggs, what would happen?

1. They would slowly turn green like an old statue in a park — no support
2. They would tarnish faster from the sulphur gases — ✓ the right answer · no support
3. They would start rusting orange — no support
4. They would stay shiny forever — ← Mova's choice · score 2

Why: It took the question to ask what happens next. It chose option 4 with score 2, the only option with support. Its support: lesson 10, line 9: «Caramel is sugar broken down by strong heat into new substances; hot caramel is much hotter than boiling water and sticks to skin.», reached through what followed the sentence the question matched. What matched: the same action «stick» (+4). Against it: a different doer (counts against) (-2). The right option, 2, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

Test 7 · ★ · right ✓

In a cartoon, a scientist leaves a lump of sodium on the desk and goes for lunch. What would really happen?

1. It would react with the air within seconds — ← Mova's choice · ✓ the right answer · no support
2. It would slowly go green over years — no support
3. Nothing at all, sodium is as calm as gold — no support
4. It would just collect a bit of dust — 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 ✗

"dropped vinegar on me dad's fancy knife and it got dark spots. is it ruined?" What's going on?

1. Acid reacted with carbon steel; dry knives fast — ✓ the right answer · no support
2. The knife is rusting from the inside out — ← Mova's choice · score 6
3. The steel is slowly turning into silver — no support
4. The vinegar made the knife magnetic — score 6

Why: It took the question to ask who or what does it. It chose option 2 with score 6, tied with another option at 6 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 14, line 17: «Carbon steel knives (not stainless) get dark spots when left wet with acid such as vinegar, so chefs dry them at once.», reached through the remembered sentence the question matched. What matched: it fills the role the question asks for (+4); the same doer «steel knives» (+2). The right option, 1, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

Test 9 · ★ · wrong ✗

Which object would you expect to look the same after a hundred years in a church?

1. A bright new copper church roof — ← Mova's choice · no support
2. A gold-leaf picture frame — ✓ the right answer · no support
3. A silver candlestick on the altar — no support
4. A big bronze bell in the tower — 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 ✓

Teacher: "a cut apple and a cut bit of metal both change in air". What makes both happen?

1. Water from the air freezing on them — no support
2. Oxygen in the air reacting with them — ← Mova's choice · ✓ the right answer · score 5
3. Light from the windows bleaching them — no support
4. Germs from the air eating them — no support

Why: It took the question to ask who or what does it. It chose option 2 with score 5, the only option with support. Its support: lesson 14, line 12: «Oxygen is a very reactive gas; a cut apple and a cut piece of some metals both change colour in air, in very different ways.», reached through the same lesson line as the sentence the question matched. What matched: it fills the role the question asks for (+3); the same doer «oxygen» (+2). · the question and its options parsed, with trees and pragmatics

Exam question 1 · formal language · wrong ✗

Identify the principal cause of the darkening of silver tableware in ordinary domestic conditions.

1. Absorption of moisture from the atmosphere — ← Mova's choice · no support
2. Reaction with sulphur-containing gases in the air — ✓ the right answer · no support
3. Contact with oxygen alone in dry air, as in the rusting of iron — no support
4. Exposure to excessive quantities of light — 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 2 · formal language · right ✓

Which of the following statements most accurately characterises the chemical behaviour of gold in air?

1. It undergoes almost no reaction and does not tarnish — ← Mova's choice · ✓ the right answer · no support
2. It reacts rapidly and must be stored under oil — no support
3. It acquires a green protective patina over time — no support
4. It is converted into rust within a few years — 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 ✓

It is given that a ring containing copper produces a green mark upon the skin of its wearer. Select the response consistent with the established facts.

1. The mark denotes poisoning of the blood and requires urgent medical treatment — no support
2. The mark results from the ring absorbing iron from the blood — no support
3. The mark results from sweat reacting with the copper and is harmless — ← Mova's choice · ✓ the right answer · score 3
4. The mark is permanent and cannot be washed away — score 2

Why: It took the question to ask which statement is true. It chose option 3 with score 3, against 2 for the next best. Its support: lesson 14, line 10: «A cheap ring with copper in it can leave a harmless green mark on skin, because sweat with its salt and acid reacts with the copper; the mark simply washes off.», reached through a sentence linked to the one the question matched. What matched: the same action «react» (+2); the same circumstance (+2). Against it: a different doer (counts against) (-1). · the question and its options parsed, with trees and pragmatics

Exam question 4 · formal language · wrong ✗

Determine which of the following assertions concerning cola is consistent with the established facts.

1. It does not dissolve a tooth overnight, yet sugary acidic drinks harm teeth over time — ✓ the right answer · no support
2. It contains no acid whatsoever and is harmless to teeth — ← Mova's choice · score 3
3. It dissolves a human tooth completely within a single night — no support
4. It strengthens tooth enamel when consumed daily — no support

Why: It took the question to ask which statement is true. It chose option 2 with score 3, the only option with support. Its support: lesson 14, line 16: «Cola has a weak acid that slowly loosens rust on a nail; the story that cola dissolves a tooth overnight is a myth, though sugary acid drinks do harm teeth ove…», reached through the option's own match among the sentences about the question's things. What matched: the same thing acted on «weak acid» (+2); the same doer «cola» (+1). The right option, 1, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

This page in Markdown → https://md.mova.elamur.ai/free/en/school-run/chemistry/14-tarnish-and-how-metals-change/