Question

A solution contains 29.1g per litre of aluminium Sulphate. Calculate the number of Sulphate ions in 350cm³ of the solution.(Al = 27, S = 32, O = 16) Avogadro’s constant = 6.0 x 10^23.

Answer 1

Molar mass of Al₂(SO₄)₃ = 27 x 2 + (32 x 3) + (16 x 4 x 3) = 342
Moles of Al₂(SO₄)₃ in 1000cm³ = 
Moles of Al2(SO₄)₃ in 350cm³ =
Al₂(SO₄)_3(aq) →2Al³⁺_(aq) + 3SO₄^2-_(aq)
1 mole of Al₂(SO₄)₃ produce 3 moles of SO₄^2- ions
0.02979 moles → 0.02979 x 3 moles of SO42- ions
Number of SO₄^2- ions = 0.08937 x 6.0 x 10²³ = 5.36 x 10²² ions.