Question

The mass of water in one mole of crystalline hypo is
A.18. B.90. C.158. D.248

Answer 1

The formula of crystalline hypo is Na2S2O3.5H2O

So it contains 5 moles of water.Hence mass of water present in crystalline hypo is 5*18 =90

Answer 2

The mass of water in one mole of crystalline hypo is 90.

Explanation:

Molar mass of atomic substance is numerically equal to its atomic mass in amu.

molar mass of an atom(g)=atomic mass(amu)  

The chemical formula of crystalline hypo is $\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}$

Molar mass of $H_2O$ molecule = 2 (molecular weight of hydrogen) + 1 (molecular weight of oxygen)

$=2(1)+(16)$

$\text { Molar mass of H2O molecule } =18 \ \mathrm{g} / \mathrm{mol}$

Crystalline hypo has water in five moles.

Hence, mass of water in one mole of crystalline hypo =5 $\times$ 18 = 90