Question

$ 1 \,g $ of an impure sample of calcium carbonate (containing no thermally decomposable impurities) on complete thermal decomposition gave $ 0.33 \,g $ of carbon dioxide gas. The percentage of impurity in this sample is (Atomic masses of $ C $ , $ O $ and $ Ca $ are respectively $ 12,16 $ and $ 40 \,g \,mol^{-1} $ )

• A. $ 25 $
• B. $ 20 $
• C. $ 30 $
• D. $ 33 $

Answer 1

Answer: (A)

$\underset{\text{100 g}}{{CaCO_{3}}}\xrightarrow{\Delta }CaO+\underset{\text {44 g}}{{CO_{2}}}$
$44 \,g$ of $CO_{2}$ is obtained from $100\,g$ of $CaCO_{3}$
$\therefore 0.33\,g$ of $CO_{2}$ is obtained from $\frac{100}{44}\times 0.33$
$=0.75\,g$ of $CaCO_{3}$
$\therefore $ Percentage of impurity in the sample of $CaCO_{3}$ is $25\%$