Question

Which of the following statements is/are correct?

• A. A sample of $CaC{O}_3$ contains $Ca=40\%,C=12\%$ and $O=48\%$. If the law of constant composition is true, then the mass of $Ca$ in $10$ g of $CaC{O}_3$ from another source is $4.0$ g.
• B. $12$ g of carbon is heated in vacuum and there is no change in the mass. This is the best example of the law of conservation of mass.
• C. Air is heated at constant pressure and there is no change in mass but the volume increases. This is the best example of the law of conservation of mass.
• D. $S{O}_2$ gas was prepared by (i) heating $Cu$ with conc. $H_{2}S{O}_4$ (ii) burning sulphur in oxygen (iii) reacting sodium sulphite $\left(N{a}_{2}S{O}_3\right)$ with dilute $H_{2}S{O}_4$. It was observed that is each case, $S$ and $O$ combine in the ratio of $1:1$. This data illustrates the law of constant composition.

Answer 1

Answer: (A), (D)

The correct options are
A A sample of $CaC{O}_3$ contains $Ca=40\%,C=12\%$ and $O=48\%$. If the law of constant composition is true, then the mass of $Ca$ in $10$ g of $CaC{O}_3$ from another source is $4.0$ g.
D $S{O}_2$ gas was prepared by (i) heating $Cu$ with conc. $H_{2}S{O}_4$ (ii) burning sulphur in oxygen (iii) reacting sodium sulphite $\left(N{a}_{2}S{O}_3\right)$ with dilute $H_{2}S{O}_4$. It was observed that is each case, $S$ and $O$ combine in the ratio of $1:1$. This data illustrates the law of constant composition.

(A) A sample of $CaC{O}_3$ contains $Ca=40\%$, $C=12\%$ and $O=48\%$. If the law of constant composition is true, then the mass of $Ca$ in $10$ g of $CaC{O}_3$ from another source is $\frac{40\times 10}{100}=4.0$ g

According to the law of constant composition, all samples of a given chemical compound have the same elemental composition by mass.
Hence, statement A is true.

(B) $12$ g of carbon is heated in vacuum and there is no change in the mass. This is not the best example of the law of conservation of mass as there is no chemical transformation involved since there is a vacuum.

The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made and pure substances can be decomposed but the total amount of mass remains constant.

Hence, statement B is false.

(C) Air is heated at constant pressure and there is no change in mass but the volume increases. This is not the best example of the law of conservation of mass as there is no chemical transformation involved.

The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made and pure substances can be decomposed but the total amount of mass remains constant.
Hence, statement C is false.

(D) $S{O}_2$ gas was prepared by (i) heating $Cu$ with conc. $H_{2}S{O}_4$ (ii) burning sulphur in oxygen (iii) reacting sodium sulphite $\left(N{a}_{2}S{O}_3\right)$ with dilute $H_{2}S{O}_4$. It was observed that is each case, S and O combine in the ratio of $1:1$. This data illustrates the law of constant composition.

According to the law of constant composition, all samples of a given chemical compound have the same elemental composition by mass.

Hence, statement D is true.