Solutions

Question

Calculate molarity and molality of 13% solution (by weight of sulphuric acid. Its density is 1.020 g cm^–3. (At. mass, H = 1,16, S = 32 amu).

Solution

Answer:

13 % of solution of sulphuric acid contains 13 g of H₂SO₄in 100 g of the solution. Weight of water = 100 - 13 = 87 g.

mole of H₂SO₄ = 13/98 mole

Volume of H₂SO₄ solution + Weight of soluton / Density = 100/1.02 ml

= 100 / 1.02 x 1/1000 = 1/1.02 litre

Molarity of H₂SO₄ solution = mole of H₂SO₄ / Volume of solution

= 13/98 / 1/1.02 = 10.2 x 13/98 = 1.353 M

Molality of H₂SO₄ solution = mole of H₂SO₄ / wt of water in kg. = 13/98 / 87/1000 = 13/98 x 1000/87

= 1.525 mol kg^-1 (mole Kg^-1)