Question

What is the formula that demonstrates the law of multiple proportions?

Answer 1

Law of multiple proportions are also known by the name Dalton’s law by the name of scientist John Dalton which first expressed it. This states that if two elements form more than one compound present between them then the ratios of the masses of the second element which combine with a fixed mass of the first element will always be ratios of small whole numbers.

Complete answer:
The Law of Multiple Proportions generally deals with those elements which form more than one compound which states that the masses of one element which combine with a fixed mass of the second element are in a small whole number ratio.
This can be explained by taking the example of carbon and oxygen which react to form two compounds.
Let us suppose in the first compound A 42.9 g of carbon reacts with 57.1 g of oxygen and in the second compound B 27.3 g of carbon reacts with 72.7 g of oxygen.
Now we have to calculate the mass of oxygen in each compound which reacts with 1 g of carbon.
So, in Compound A, mass of Oxygen will be
$C{{O}_{2}}$
in Compound B, mass of oxygen will be
$1g\ \text{C }\times \text{ }\dfrac{72.7\ g\ O}{27.3\,g\ \text{C}}=2.66g\ \text{O}$
Now the ratio can be calculated as
$\dfrac{Mass\ \text{of O in compound B}}{Mass\ \text{of O in compound A}}=\dfrac{2.66}{1.33}=2$
This suggests that masses of oxygen that combine with a fixed mass of carbon are in 2:1 ratio.

Note:
In case of constant proportions the ratio of the compounds is always a whole number. In the given example the ratio is 2:1 which suggests that the simplest formula shown by the compound is $C{{O}_{2}}$or we can say that it is example like ${{A}_{2}}B$.