Question

x grams of $CaC{O}_3$ was completely decomposed. The mass of the solid residue formed is $28\text{g}$. What is the value of ‘x’ in grams?

• A. $44$
• B. $200$
• C. $150$
• D. $50$

Answer 1

The correct option is D $50$

$\underset{100\text{g}}{CaC{O}_3\left(s\right)}\to \underset{56\text{g}}{CaO\left(s\right)}+C{O}_2\left(g\right)$

1 mol of $CaO$ will be obtained by the decomposition of 1 mol of $CaC{O}_3$, i.e.
$56\text{g}$ of $CaO$ will be obtained from $100\text{g}$ $CaC{O}_3$.
$\therefore 28\text{g}$ residue will be formed from $\frac{28\times 100}{56}=50\text{g of}CaC{O}_3$