$x$ grams of calcium carbonate was completely burnt in air. The weight of the solid residue formed is $28…
$x$ grams of calcium carbonate was completely burnt in air. The weight of the solid residue formed is $28 \mathrm{~g}$. What is the value of $x$ (in grams)?
44
200
150
50
Solution
$\begin{array}{lc}
\mathrm{CaCO}_3(s) \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}(s)+\mathrm{CO}_2(\mathrm{~g}) \\
40+12+48 & 40+16 \\
=100 & =56
\end{array}$
$\therefore \quad 56 \mathrm{~g} \mathrm{CaO}$ is obtained from
$=100 \mathrm{~g} \cdot \mathrm{CaCO}_3$
$\therefore \quad 28 \mathrm{~g} \mathrm{CaO}$ is obtained from $=\frac{100 \times 28}{56}$
$=50 \mathrm{~g} \cdot \mathrm{CaCO}_3$