Question

If the percentage of water of crystallization in $MgS{O}_4.x{H}_{2}O$ is $13\%$, then what is the value of $x$?

• A. $1$
• B. $4$
• C. $5$
• D. $7$

Answer 1

Answer: (A)

$1$

The molar mass of $MgS{O}_4$ is $120.4$ g/mol.

The molar mass of $MgS{O}_4.x{H}_{2}O$ is $120.4+18x$ g/mol.

Thus, $1$ mole of $MgS{O}_4.x{H}_{2}O$ weighs $120.4+18x$ g and contains $18x$ g water.

But, the percentage of water of crystallization in $MgS{O}_4.x{H}_{2}O$ is $13\%$.

Hence, $\frac{13\times (120.4+18x)}{100}=18x$

or, $120.4+18x=138.4x$

or, $120.4x=120.4$

$\therefore x=1$

Thus, the value of $x$ is $1$.

Hence, the correct option is $A$