Question

6: Suppose 50.0 g of pure potassium hydroxide is dissolved in 250.00 mL water ( Solvent: -0.9987 g/mL). Given the density of the solution is 1.020 g/mL, what will be the molarity of the solution. (Hint: You need to find the volume of the solution)

Answer 1

mass of water = density of water * volume of water
= 0.9987 g/mL * 250.00 mL
= 249.675 g

mass of solution = mass of KOH + mass of water
= 50.0 g + 249.675 g
= 299.675 g

volume of solution = mass of solution / density of solution
= 299.675 g / 1.020 g/mL
= 293.799 mL

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)= 50.0 g

use:
number of mol of KOH,
n = mass of KOH/molar mass of KOH
=(50 g)/(56.11 g/mol)
= 0.8911 mol
volume , V = 293.799 mL
= 0.293799 L


use:
Molarity,
M = number of mol / volume in L
= 0.8911/0.293799
= 3.033 M
Answer: 3.03 M