Copper oxide was prepared by the following methods : (a) In one case, 1.75 g of the metal were dissolved in nitric acid and igniting the residual copper nitrate yielded 2.19 g of copper oxide. (b) In the second case, 1.14 g of metal dissolved in nitric acid were precipitated as copper hydroxide by adding caustic alkali solution. The precipitated copper hydroxide after washing, drying and heating yielded 1.43 g of copper oxide. (c) In the third case, 1.45 g of copper when strongely heated in a current of air yielded 1.83 g ofcopper oxide. Show that the given data illustrate the law of constant composition.

Copper oxide was prepared by the following methods : (a) In one case,

1.	Copper oxide was prepared by the following methods : (a) In one case, 1.75 g of the metal were dissolved in nitric acid and igniting the residual copper nitrate yielded 2.19 g of copper oxide. (b) In the second case, 1.14 g of metal dissolved in nitric acid were precipitated as copper hydroxide by adding caustic alkali solution. The precipitated copper hydroxide after washing, drying and heating yielded 1.43 g of copper oxide. (c) In the third case, 1.45 g of copper when strongely heated in a current of air yielded 1.83 g ofcopper oxide. Show that the given data illustrate the law of constant composition.
Answer» Solution :Step 1. In the FIRST experiment. 2.19 g of copper OXIDE contained 1.75 g of Cu. `therefore"100 g of copper oxide contained Cu"=(1.75)/(2.19)xx100=79.91g`, i.e., `%" of Cu"= 79.91` Step 2. In the second experiment. 1.43 g of copper oxide contained 1.14 g of copper `therefore"100 g of copper oxide contained Cu"=(1.14)/(1.43)xx100=79.72g`, i.e., `%" of Cu"=79.72` Step 3. In the third experiment. 1.83 g of copper oxide contained 1.46 g of copper `therefore"100 g of copper oxide contained Cu"=(1.46)/(1.83)xx100=79.78g`, i.e., `%" of Cu"=79.78` THUS, the percentage of copper oxide derived from all the three exkperiments is nearly the same. Hence the above DATA illustrate the law of constant COMPOSITION.