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

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

C.The reactant mass disappears when a gas forms.

D.Only solid products are counted while checking mass.

Question 2mcq

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

A.Weigh only the precipitate after filtering.

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

C.Smell the gas released during the reaction.

D.Measure only the volume of the final liquid.

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 inertia

B.Law of reflection

C.Law of constant proportions

D.Law of multiple shadows

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.Compounds form in random mass ratios only.

D.Matter is made of tiny particles called atoms.

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?

4.4\,g

B.$15.6\,g

5.6\,g

10\,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.The law of conservation of mass is false.

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

C.Atoms lost their mass during the reaction.

D.The balance cannot measure liquids.

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

D.Elements change their symbols in different samples.

Question 8mcq

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

A.Atoms combine in any decimal ratio.

B.Atoms disappear during compound formation.

C.Only molecules of elements can form compounds.

D.Atoms combine in simple whole-number ratios.

Question 9mcq

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

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

B.It increases the mass of products.

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

D.It changes compounds into mixtures automatically.

Question 10mcq

Which control improves a classroom activity testing conservation of mass?

A.Use a bigger beaker but leave it open.

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

C.Measure only the heaviest product.

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