Question

2.75 g of cupric oxide was reduced by heating in a current of hydrogen and the weight of copper
that remained was 2.196 g. Another experiment, 2.358 g of copper was dissolved in nitric acid
and the resulting copper nitrate converted into cupric oxide by ignition. The weight of cupric
oxide formed was 2.952 g. Show that these results illustrate law of constant composition.
​

Answer 1

Answer:

First experiment

∙ Copper oxide =1.375g

∙ Copper left =1.098g

∙ Oxygen present =1.375−1.098=0.277g

Percentage of oxygen in CuO=(0.277)(100 %) 1.375=20.15 %

Second Experiment

∙ Copper taken =1.179g

∙ Copper oxide formed =1.476g

∙ Oxygen present =1.476−1.179=0.297g

Percentage of oxygen in CuO=(0.297)(100 %) 1.476=20.12 %

Percentage of oxygen is approximately (within significant figures limit) the same in both the above cases. So the law of constant composition is illustrated.

In chemistry, the law of definite proportion, sometimes called Proust's law or the law of definite composition, or law of constant composition states that a given chemical compound always contains its component elements in fixed ratio and does not depend on its source and method of preparation.