Question

A sample of pure carbon dioxide, irrespective of its source contains $27.27\%$ carbon and $72.73\%$ oxygen. The given data supports:
A) Law of constant composition
B) Law of conservation of mass
C) Law of chemical properties
D) Law of multiple proportions

Answer 1

Carbon dioxide can be obtained by different methods like heating limestone, burning of carbon, etc. As $C{O_2}$ are obtained from the different samples it contains carbon and oxygen in the ratio of $3:8$ by mass.

Complete step by step answer:
Chemical compound always contains exactly the same proportion of elements by mass irrespective of its origin.
Elemental mass of carbon is 12 $gmo{l^{ - 1}}$
and The elemental mass of oxygen is 16 $gmo{l^{ - 1}}$
Ratio by atoms in which carbon and oxygen present in $C{O_2}$ is $1:2$
So let us find the ratio by mass in which carbon and oxygen present in $C{O_2}$ :
$\dfrac{{{\text{mass of carbon}}}}{{{\text{mass of oxygen}}}} = \dfrac{{12}}{{2 \times 16}}$
Therefore the ratio by mass in $C{O_2}$ becomes $3:8$ .
Now we are given with the percentage of carbon and oxygen in $C{O_2}$:
Now let us find the ratio by percentage in which carbon and oxygen are present in $C{O_2}$ .
$\dfrac{{{\text{ carbon \% }}}}{{{\text{oxygen \% }}}} = \dfrac{{27.27}}{{72.73}}$
As both the value is divisible by we get:
$\dfrac{{{\text{ carbon }}}}{{{\text{oxygen }}}} = \dfrac{3}{8}$
So, carbon dioxide prepared by any method contains copper and oxygen in the same proportion by mass. Thus, we can say that the given data proves the law of constant proportions.
The Law of constant proportion is also known as the law of definite proportion.

Therefore, we can conclude that the correct answer to the question is option A.

Additional information: we know that the pure water obtained from river, sea, well etc. always contains hydrogen and oxygen combined together in the ratio $1:8$ by mass. So it justifies the law of constant proportion.

Note: Here you can be confused between the law of constant proportion and the law of multiple proportions. But in law of multiple proportions, two-element combines with each other to form two or more compounds.