Chemical Changes: Evidence & Conservation — Practice · Grade 6 Science

Chapter: Matter, Mixtures & Water Properties

What this practice covers

By the end of Chemical Changes: Evidence & Conservation you should be able to:

8 questions, written answer and multiple choice, each with a worked explanation.

Vocabulary used: chemical change, conservation of mass, evidence, system boundary, uncertainty.

Problem 1

What does the particle model conserve?
Answer and explanation

The number of each kind of atom. New combinations form, but the represented atoms remain accounted for.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 2

Do bubbles alone prove a new substance?
Answer and explanation

No. A physical state change can also create bubbles; the gas identity and process need further evidence.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 3

Was 4 g of matter destroyed?
Answer and explanation

No. It crossed the chosen boundary as gas. The mass inside differs from the mass of the complete accounted system.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 4

Why does a supplied record still need qualification?
Answer and explanation

The conclusion depends on the record’s stated method and boundaries; illustrative data are not proof that a real procedure was performed.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 5

Develop a complete response: Explain new combinations and conservation, then distinguish this evidence from color alone. Include relevant evidence and one method or model limit.
Answer and explanation

Two A atoms and two B atoms are represented on each side. Their combinations change from A₂ and B₂ to two AB particles. The closed-system mass remains 60 g. This model directly states a rearrangement; a color change alone would not supply the same evidence of substance identity.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 6

Apply the unit independently: An exposed metal object gains mass during a stated reaction with oxygen. Does conservation fail? Give a reason and a relevant qualification.
Answer and explanation

No. Oxygen from the surroundings enters the material. Account for both the metal and the added oxygen rather than treating the exposed object as a closed system.

Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.

Problem 7

Which statement correctly uses chemical change in Chemical Changes: Evidence & Conservation?
  1. One illustrative result establishes every real condition and needs no further evidence.
  2. Any bubbles or color change conclusively prove a chemical reaction.
  3. A mass change inside an open container means matter was destroyed.
  4. chemical change: A change that forms substances with different chemical identities.
Answer and explanation

chemical change: A change that forms substances with different chemical identities.

A change that forms substances with different chemical identities. Two A atoms and two B atoms are represented on each side. Their combinations change from A₂ and B₂ to two AB particles. The closed-system mass remains 60 g. This model directly states a rearrangement; a color change alone would not supply the same evidence of substance identity.

Problem 8

Which statement correctly uses conservation of mass in Chemical Changes: Evidence & Conservation?
  1. conservation of mass: Matter remains accounted for when the complete relevant system and exchanges are included.
  2. Any bubbles or color change conclusively prove a chemical reaction.
  3. A mass change inside an open container means matter was destroyed.
  4. One illustrative result establishes every real condition and needs no further evidence.
Answer and explanation

conservation of mass: Matter remains accounted for when the complete relevant system and exchanges are included.

Matter remains accounted for when the complete relevant system and exchanges are included. Two A atoms and two B atoms are represented on each side. Their combinations change from A₂ and B₂ to two AB particles. The closed-system mass remains 60 g. This model directly states a rearrangement; a color change alone would not supply the same evidence of substance identity.

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