Question

Barium chloride crystals contain 14.8% water of crystallisation. Find the number of molecules of water of crystallisation per molecule.

Answer 1

$BaC{l}_2.n{H}_{2}O$
Atomic mass of Ba =137 g
Atomic mass of Cl= 35.5 g
Molecular mass of $H_{2}O$ = 18
$BaC{l}_2.n{H}_{2}O$ = 137+ 71 + 18n
[208+18n] contains water = 14.8 % water in $BaC{l}_2.n{H}_{2}O$

$\%ofwater=\frac{weightofwater}{weightofsalt}\times 100$

$14.8=\frac{18n}{208+18n}\times 100$

[208+18n] contains water = $\frac{[208+18n]\times 14.8}{100}=18n$
[208+18n] contains water =$[104+9n]2\times 14.8=1800n$
$=1917\times n=3848$
$n=\frac{3848}{1917}=2.0073\approx 2$
2 molecule of water of crystallisation are present in 1 molecule of Ba$C{l}_2$