Question

If 1.4 g of calcium oxide is formed by the complete decomposition of calcium carbonate, then the amount of calcium carbonate taken and the amount of carbon dioxide formed will be respectively :
(a) 2.2 g and 1.1 g
(b) 1.1 g and 2.5 g
(c) 2.5 g and 1.1 g
(d) 5.0 g and 1.1 g

Answer 1

(c) 2.5 gm and 1.1 gm

Molecular mass of CaCO₃: 40 + 12 + (16 × 3) = 100g
Molecular mass of CaO: 40 + 16 = 56g
Molecular mass of CO₂: 12 + (16 × 2) = 44g
Reaction for the decomposition of calcium carbonate:

$\begin{array}{ccccc}{\mathrm{CaCO}}_3& \to & \mathrm{CaO}& +& {\mathrm{CO}}_2\\ 100\mathrm{g}& & 56\mathrm{g}& & 44\mathrm{g}\\ \mathrm{X}& & 1.4\mathrm{g}& & \mathrm{Y}\end{array}$

56 g of CaO is obtained when 100g of CaCO₃ is burnt.
Therefore, to get 1.4g of CaO, the amount of CaCO₃ to be burnt will be
$\frac{100\times 1.4}{56}=2.5\mathrm{g}$
For CO₂,
100g of CaCO₃ yields 44g of CO₂
Therefore, 2.5g of CaCO₃ will yield;
$\frac{44\times 2.5}{100}=1.1\mathrm{g}$