Question

find the molality and molarity of 15% solution w/w of H2SO4 ( density of H2SO4 = 1.02gcm-3 )

Answer 1

Density of given solution is 1.2 g/cm³ = 1.2 g/mL
Let the volume of solution is 1000 ml (1 L) then the mass of the solution would be :
D = M/V
Mass = density x volume
= 1.2 g/ml x 1000 ml
= 1200 g
Mass of H₂SO₄ in solution is 15 %
= 1200 g x 15/100 = 180 g
​Molar mass of H₂SO₄ = 98 g/mol
​Moles of H₂SO₄ in solution = ​180 g/​98 g mol^-1= 1.8 mol
Molarity of solution is 1.8 mol L^-1 = 1.8 M

​Mass of the solvent = 1200g - 180 g = 1020g
Moles of solute = 1.8 mol
Molality = moles of solute/solvent in Kg
= 1.8 mol /1.020 kg
= 1.76 mol kg^-1
Molality of solution is 1.76 mol kg^-1