Question

If calcium of weight $x$ g, carbon $y$ g and oxygen $z$ g, are present in $1.5$ g of calcium carbonate and if a sample of calcium carbonate from another source contains the following percentage composition: $Ca=40.0\%$, $C=12.0\%$ and $O=48.0\%$, then find the value of $x,y$ and $z$. (The law of constant composition holds true.)

• A. $x=0.6,y=0.18,z=0.72$
• B. $x=0.4,y=0.18,z=0.62$
• C. $x=0.6,y=0.2,z=0.70$
• D. None of the above

Answer 1

The correct option is A $x=0.6,y=0.18,z=0.72$

According to the law of constant composition, the samples of calcium carbonate from the two sources must be identical, i.e, their percentage composition must be the same.
Thus, the weights of $Ca,C$ and $O$ in $1.5$ g of $CaC{O}_3$ are as follows:
Calcium $\left(Ca\right)=\frac{40\times 1.5}{100}=0.60$ g

Carbon $\left(C\right)=\frac{12\times 1.5}{100}=0.18$ g

Oxygen $\left(O\right)=\frac{48\times 1.5}{100}=0.72$ g