Question

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

Answer 1

Law of constant proportion means whatever be the method of preparation of a compoundthe compoisition remains the same.

I method

Weight of copper oxide = 2.75 g

Weight of copper   = 2.196 g

2.75 g of the copper oxide contained 2.196 g of the metal

100 g of the  copper oxide contained = 2.196/2.75 x 100 = 79.86 %

II method

2.952 g of copper oxide contains 2.358 g of copper

100 g of the  copper oxide contained = 2.358/2.952 x 100 = 79.87 %

For the law of constant proportion, the % obtained should be same in both the methods.