Question

Which of the statements are true about the law of chemical combination?

• A. Potassium combines with two isotopes of chlorine (${}^{35}Cl$ and ${}^{37}Cl$) to form two samples of $KCl$. Their formation follows the law of definite composition.
• B. Different proportions of oxygen in the various oxides of sulphur proves the law of multiple proportions.
• C. $H_{2}O$ and $H_{2}S$ contain $11.11\%$ hydrogen and $5.88\%$ hydrogen respectively whereas $S{O}_2$ contains $50\%$ sulphur. The above data prove the law of reciprocal proportions.
• D. In the decomposition of $N{H}_3(2N{H}_3\stackrel{\Delta }{\to }{N}_2+3H_2)$, the ratio of volumes of $N{H}_3,N_2$ and $H_2$ is $2:1:3$. The above data proves the Gay Lussac's law.

Answer 1

Answer: (B), (C), (D)

$H_{2}O$ and $H_{2}S$ contain $11.11\%$ hydrogen and $5.88\%$ hydrogen respectively whereas $S{O}_2$ contains $50\%$ sulphur. The above data prove the law of reciprocal proportions.
Different proportions of oxygen in the various oxides of sulphur proves the law of multiple proportions.
In the decomposition of $N{H}_3(2N{H}_3\stackrel{\Delta }{\to }{N}_2+3H_2)$, the ratio of volumes of $N{H}_3,N_2$ and $H_2$ is $2:1:3$. The above data proves the Gay Lussac's law.

(A) Potassium combines with two isotopes of chlorine (${}^{35}Cl$ and ${}^{37}Cl$) to form two samples of $KCl$. Their formation does not follow the law of definite composition as the proportion of chlorine in two samples are different.
Hence, the statement A is false.

(B) Different proportions of oxygen in the various oxides of sulphur prove the law of multiple proportions.
This is because the ratio of masses of oxygen that combine with same mass of sulphur (to form $S{O}_2$ and $S{O}_3$) is $2:3$, a simple ratio.
Hence, the statement B is true.

(C) $H_{2}O$ and $H_{2}S$ contain $11.11\%$ hydrogen and $5.88\%$ hydrogen respectively whereas $S{O}_2$ contains $50\%$ sulphur. The above data proves the law of reciprocal proportions.
According to the law of reciprocal proportions, "If two different elements combine separately with the same weight of a third element, the ratio of the masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine."
Hence, the statement C is true.

(D) In the decomposition of $N{H}_3(2N{H}_2\stackrel{\Delta }{\to }{N}_2+3H_2)$, the ratio of volumes of $N{H}_3,N_2$ and $H_2$ is $2:1:3$. The above data proves the Gay Lussac law.
According to the Gay Lussac law, "The ratio between the volumes of the reactant gases and the products can be expressed in simple whole numbers."
Hence, the statement D is true.