One deciliter solution consists of 200 mg of KMnO4, and the density of the solution is found to be 1.037 g/mL. What is the molarity and the molality of the solution?

Answer 1

What is a deciliter? It is 0.1 liters.

0.1 L x 1000 ml/L = 100 ml

100 ml x 1.037 g/ml = 103.7 g = mass of the solution

Since there are 200 mg KMnO4 (0.200 g) the rest must be water. Mass water = 103.7 g - 0.2 g = 103.5 g H2O

Molality = moles KMnO4/kg H2O

moles KMnO4 = 0.2 g x 1 mol/158g = 0.00127 moles

kg H2O = 103.5 g x 1 kg/1000 kg = 0.1035 kg

Molality (m) = 0.00127 moles/0.1035 kg = 0.0123 m = 0.01 m (1 sig. fig. based on 1 sig fig in 200 mg)

Molarity = moles KMnO4/L solution

moles KMnO4 = 0.00127 moles

Liters of solution = 0.1

Molarity (M) = 0.00127 mol/0.1 L = 0.0127 M = 0.01 M (1 sig. fig.)