Question

What is the molal and molarity concentration of a 98.0 mass percent aqueous sulfuric acid solution. The density of the solution is 1.83 g/mL.

Answer 1

Solution:

Molarity = mol solute / volume of solution in L

Molality = mol solute / mass of solute in kg

Calculation of moles of solute = mass in g /molar mass

Here solute is H2SO4 .

Lets assume volume of solution is 1.0 L

Mass of percent of H2SO4 in water is 98 %

Calculation of mass of solution = 1.0 L x (1000 mL / 1 L ) x 1.83 g / mL = 1830 g H2SO4

Mol H2SO4 = (1830 g x 98.0 /100) / 98.079 g mol^-1 = 18.3 mol H2SO4

Mass of water = 1830 g – mass of H2SO4 in g = 1830 g – 1793.4 g = 36.6 g

Mass of water in kg = 36.6 g = 0.0366 kg

Molarity = 18.3 mol H2SO4 / 1.0 L = 18.3 M

Molality = 18.3 mol / 0.0366 kg = 499.6 molal