A sample of hydrated sodium phosphate has a mass of 190 g. Of this, 108 g is the mass of water of crystallization. What is the molar mass of the hydrated sodium phosphate ?

(Atomic mass of $\text{Na}=23\text{u},\text{P}=31\text{u},\text{O}=16\text{u},\text{H}=1\text{u}$ )

Weight of compound is 190 g.

Mass of water of crystallisation  is 108g

$\to$  weight of ${\text{Na}}_3{\text{PO}}_4\text{is}190-108=82g$

1 mole of $N{a}_{3}P{O}_4-164g$

So, 82g will be $0.5{\text{ moles of Na}}_3{\text{PO}}_{\text{4}}$

$\text{for}\text{1}\text{mole}{\text{Na}}_{\text{3}}{\text{PO}}_{\text{4}}\text{,water}\text{of}\text{Crystallization}\text{is}2\times 108\text{g}$

Finally 1 mole hydrated ${\text{Na}}_3{\text{PO}}_4$  is heating

$={\text{Na}}_3{\text{PO}}_4+\text{Water of crystallization}$

$=164+216=380$ g/mol