Question

1.375g of CuO was reduced by hydrogen and 1.098g Cu was
obtained. In another experiment, 1.178g of Cu was dissolved in nitric
acid and the resulting copper nitrate was converted into CuO by
ignition. The weight of CuO formed was 1.476g. Show that these
results prove the law of constant composition
'

Answer 1

In first experiment:

Copper oxide = 1.375 g

Copper left = 1.098 g

Therefore oxygen present = 1.375 – 1.098g = 0.277 g

Second experiment:

Copper taken = 1.179 g

Copper oxide formed = 1.476 g

Therefore oxygen present = 1.476-1.179g = 0.297 g

Since percentage of oxygen is the same in both the above cases, so the law of constant composition is illustrated.

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Answer 2

Answer:

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  

0.277

1.098

​  

=3.9:1≃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  

0.272

1.176

​  

=4.3:1≃4:1.

Explanation: