Question

Concentrated KOH is 45.0% KOH by mass and has a density of 1.45 g/mL. What is the molar concentration of concentrated potassium hydroxide?

Answer 1

Let volume of solution be 1 L

volume , V = 1 L

= 1*10^3 mL

density, d = 1.45 g/mL

mass = density * volume

= 1.45 g/mL *1*10^3 mL

= 1450 g

This is mass of solution

mass of KOH = 45.0 % of mass of solution

= 45.0*1450/100

= 652.5 g

Molar mass of KOH,

MM = 1*MM(K) + 1*MM(O) + 1*MM(H)

= 1*39.1 + 1*16.0 + 1*1.008

= 56.108 g/mol

mass(KOH)= 652.5 g

number of mol of KOH,

n = mass of KOH/molar mass of KOH

=(652.5 g)/(56.108 g/mol)

= 11.63 mol

volume , V = 1 L

Molarity,

M = number of mol / volume in L

= 11.63/1

= 11.63 M

Answer: 11.6 M