Question

He mole fraction of potassium nitrate in an aqueous solution is 0.0194. The solution's density is 1.0627 g/ml. Calculate the molarity of the solution.

Answer 1

The solution contains potassium nitrate (KNO3) in water (H2O)

The molar mass of KNO3 = 101 g/mol

The molar mass of H2O = 18 g/mol

Mole fraction of KNO3 = 0.0194

Therefore mole fraction of H2O = 1 - 0.0194 = 0.9806

Total mass of the solution = KNO3 + H2O

= 0.0194 moles * 101 g/mol + 0.9806 moles * 18 g/mol

= 1.9594 g + 17.6508 = 19.6102 g

Volume of the solution = Mass of solution/density

= 19.6102 g/ 1.0627 g.ml-1 = 18.453 ml = 0.01845 L

Molarity of KNO3 = moles of KNO3/volume of solution

= 0.0194 mole/0.01845 L = 1.05 M