Question

Carbon is found to form two oxides which contain 42.9% and 27.3% of carbon respectively. The above data supports:

• A. Law of constant proportion
• B. Law of multiple proportion
• C. Law of reciprocal proportion
• D. None of these

Answer 1

The correct option is B Law of multiple proportion

I. Calculating the percentage composition of carbon and oxygen in each of the two oxides.
$\begin{array}{cccc}& \text{First oxide}& \text{Second oxide}& \\ \text{Carbon}& 42.9\%& 27.3\%& \text{(Given)}\\ \text{Oxygen}& 57.1\%& 72.7\%& \end{array}$

II: Calculating the masses of carbon which combine with a fixed mass i.e., one part by mass of oxygen in each of the two oxides.
In the first oxide, 57.1 parts by mass of oxygen combine with carbon which is equal to 42.9 parts.
$\therefore$ 1 part by mass of oxygen will combine with carbon $=\frac{42.9}{57.1}=0.751$
In the second oxide 72.7 parts by mass of oxygen combine with carbon = 27.3 parts
$\therefore$ 1 part by mass of oxygen will combine with carbon $=\frac{27.3}{72.7}=0.376$

III: Comparing the masses of carbon which combine with the same mass of oxygen in both the oxides.
The ratio of the masses of carbon that combine with the same mass of oxygen (1 part) is 0.751 : 0.376 or 2 : 1
Since this is a simple whole number ratio, the above data illustrates the law of multiple proportions.