The mole fraction of water in a sulphuric acid solution is 0.85. What is the molality of the solution? 

9.8

Mole fraction of water = 0.85

Mole fraction of H₂SO₄ in solution = 1 - 0.85 = 0.15

If n₁ is the the number of moles of water and n₂ is the no of moles of H₂SO₄ in solution.

Molality of solution means moles of H₂SO₄ present in 1000 g of water

n₁ = \(\frac{1000}{18}\) = 55.55, n₂ = ?

Mole fraction of H₂SO₄ = \(\frac{n_2}{55.55 + n_2}\) 

0.15 = \(\frac{n_2}{55.55 + n_2}\)

0.15 n₂ + 8.3325 = n₂

8.3325 = 0.85 n₂

n₂ = \(\frac{8.3325}{0.85}\) = 9.8 m