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, $1.179$ 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. The result of this process show :

• A. law of reciprocal proportion
• B. law of multiple proportion
• C. law of constant proportion
• D. none of these

Answer 1

The correct option is C law of constant proportion

According to the law of constant proportion, "A chemical compound always contains the same elements combined together in the same proportion by mass."
1.375 g of cupric oxide contains 1.098 g copper and $1.375-1.098=0.277$ g oxygen.
The ratio of copper to oxygen is $\frac{1.098}{0.277}=3.9:1\simeq 4:1$.
1.4479 g of cupric oxide contains 1.176 g copper and $1.4479-1.176=0.272$ g oxygen.
The ratio of copper to oxygen is $\frac{1.176}{0.272}=4.3:1\simeq 4:1$.