Question

State law of constant proportion. In magnesium oxide, magnesium and oxygen are prsent inthe ratio of 3:2 by mass. In a chemical reaction 6g magnesium poder was ignited in a container having 12g of pure oxygen. After the completion of the chemical reaction, it was found the 8g of oxygen was left unreacted. Showthat these observations are in accordance wth the law of consatnt proportions

Answer 1

LAW OF CONSTANT PROPORTION:
Law of constant proportion states that a given compound always contains exactly that same proportion of elements by weight.

We are given that the mass ratio of Mg O is 3:2
That means 3 gm of Mg will react with 2 gm of O to form MgO

since we have 6gm of Mg and excess of oxygen, Mg becomes a limiting reagent.

since 3 gm of Mg will react with 2 gm of O

         6 gm of Mg will react with 4 gm of O .

But we have 12 gm of O , so 12-4=8 gm will be remaining.

Thats exactly according to the law of definite proportion given by Joseph Proust.