Question

A 6.90 M solution of KOH in water contains 30% by weight of KOH. What is the density of the solution?

Answer 1

Given: Molarity (M) = 6.90 mol/L

Weight % of KOH = 30%

Molar mass of KOH = 56 g/mol

We need to find the density of the solution (in g/mL).

Let 1 L = 1000 mL of solution

Moles of KOH = 6.90 mol

Mass of KOH = 6.90 × 56 = 386.4 g

Weight % = `"Mass of solute"/"Mass of solution" xx 100`

`30 = 386.4/"Mass of solution" xx 100`

Mass of solution = `(386.4 xx 100)/30`

= 1288 g

Density = `"Mass of solution"/"Volume"`

= `1288/1000`

= 1.288 g/mL