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.
Hint : In first case % of oygen in $CuO=20.14$% .In second case % of oxygen in $CuO=20.14$%

Answer 1

Law of constant proportion means whatever be the method of preparation of compound the composition remains the same

case1 :

mass of copper oxide=2.75g

mass of copper=2.196g

% of copper = 2.196*100/2.75=79.85%

% of oxygen=100-79.85=20.1%

case2:

mass of copper oxide =2.952g

mass of copper= 2.358g

%of copper=2.358*100/2.952=79.87%

% of oxygen =100-79.87=20.1%.

Since % of Cu Oxygen is the same in both the experiments, hence the law of constant composition is proved.