Question

The solubility of Ba(OH)₂.8H₂O in water at 288 K is 5.6g per 100 g of water. What is morality of hydroxide ions in saturated solution of barium hydroxide at 288 K?(atomic masses:Ba - 137,O-16,H-1)

Answer 1

The molecular mass of Ba(OH)₂ = 315.4639 g/mol
Given that,
5.6g in 100g of water, which is the same as 56 g in 1kg of water.
Therefore, the number of moles of Ba(OH)₂ in 1kg of water =$\frac{56}{315.4639}$ = 0.1775 moles
The dissociation of Ba(OH)₂ is as follows.

$Ba\left(OH\right){}_2.8H_{2}O⟶B{a}_{\left(aq\right)}^{2{+}^{}}+O{H}_{\left(aq\right)}^{+}+8H_2{O}_{\left(l\right)}$

As specified in the balanced equation,
1 mol of $Ba{\left(OH\right)}_2$ produces 2 moles of OH^- ions.
Hence, No of moles of OH^- ions = $2\times 0.177=0.355moles$As molality is moles of solute per kilogram of solvent,

Molality of OH^- ions = 0.355 moles