Question

$1.375$ g of cupric oxide was reduced by heating in a current of hydrogen and the weight of copper obtained was $1.098$ g. In another experiment, $1.156$ g of copper was dissolved in nitric acid and the resulting solution was evaporated to dryness. The residue of copper nitrate when strongly heated was converted into $1.4476$ g of cupric oxide. State the law illustrated by these chemical combinations.

• A. Law of reciprocal proportion
• B. Law of multiple proportion
• C. Law of constant composition
• D. None of these

Answer 1

Answer: (C)

Law of constant composition

Law of constant composition states that all samples of a given chemical compound have the same elemental composition by mass.

Here, in the first experiment, 1.375 g of cupric oxide was reduced by heating in a current of hydrogen and the weight of copper obtained was 1.098 g.

1.375 g of cupric oxide has 1.098 g of copper and $1.375-1.098=0.277$ g of oxygen.

Copper and oxygen are in the ration $\frac{1.098}{0.277}=\frac{1}{4}$.

In the second experiment, 1.156 g of copper was dissolved in nitric acid to form copper nitrate, which on strongly heating got converted into 1.4476 g of cupric oxide.

=1.4476 g of cupric oxide has 1.156 g of copper and $1.4476-1.156=0.2911g$ oxygen.

Copper and oxygen are in the ratio $\frac{1.156}{0.2911}=\frac{1}{4}$.

This means whatever may be the source of a compound, it has the same elemental composition by mass in all samples.