Homework Practice

Printable assignment

Atoms and Molecules: Laws That Explain Chemical Change

Section A: Core Ideas

Question 1mcq

A closed flask contains reactants before a chemical reaction and products after it. Which observation supports the law of conservation of mass?

A.Only solid products are counted while checking mass.

B.The total mass before and after the reaction remains the same.

C.The product mass is always greater than the reactant mass.

D.The reactant mass disappears when a gas forms.

Question 2mcq

Which setup best verifies conservation of mass in the reaction between barium chloride and sodium sulphate solutions?

A.Weigh the closed container before mixing and after precipitate formation.

B.Measure only the volume of the final liquid.

C.Smell the gas released during the reaction.

D.Weigh only the precipitate after filtering.

Question 3mcq

Water from any pure source always contains hydrogen and oxygen in the mass ratio

1:8

. Which law does this support?

A.Law of multiple shadows

B.Law of reflection

C.Law of inertia

D.Law of constant proportions

Question 4mcq

Which statement agrees with Dalton atomic theory?

A.Atoms of one element have different chemical symbols.

B.Atoms are visible to the naked eye.

C.Matter is made of tiny particles called atoms.

D.Compounds form in random mass ratios only.

Question 5mcq

10\,g

of calcium carbonate gives

5.6\,g

of calcium oxide and carbon dioxide, what mass of carbon dioxide is produced in a closed system?

5.6\,g

4.4\,g

10\,g

D.$15.6\,g

Section B: Application Practice

Question 6mcq

A student finds lower mass after an open-vessel reaction that releases gas. What is the best conclusion?

A.Gas may have escaped, so the activity did not properly test conservation of mass.

B.Atoms lost their mass during the reaction.

C.The balance cannot measure liquids.

D.The law of conservation of mass is false.

Question 7mcq

Two samples of pure carbon dioxide contain carbon and oxygen in the same fixed mass ratio. What does this show?

A.A compound has different composition in different places.

B.A mixture always has a fixed formula.

C.Elements change their symbols in different samples.

D.A compound has fixed composition, regardless of its source.

Question 8mcq

According to Dalton atomic theory, why does a compound have a fixed composition?

A.Atoms disappear during compound formation.

B.Atoms combine in any decimal ratio.

C.Atoms combine in simple whole-number ratios.

D.Only molecules of elements can form compounds.

Question 9mcq

Why is a closed container preferred when demonstrating conservation of mass with a reaction that produces gas?

A.It changes compounds into mixtures automatically.

B.It prevents gas from escaping, so total mass can be measured accurately.

C.It allows atoms to be created inside the container.

D.It increases the mass of products.

Question 10mcq

Which control improves a classroom activity testing conservation of mass?

A.Use a sealed apparatus and measure the same complete system before and after reaction.

B.Add extra water after the reaction to match mass.

C.Measure only the heaviest product.

D.Use a bigger beaker but leave it open.