Al2(So4)3 its solubility =6.2×10^-3? Calculate solubility product?

Molar mass of Al₂(SO₄)₃ = (27.0×2 + 32.1×3 + 16.0×12) g/mol = 342.3 g/mol
Solubility of Al₂(SO₄)₃ = (6.2 × 10⁻³ g/L) / (342.3 g/mol) = 1.81 × 10⁻⁵ mol/L


__________ Al₂(SO₄)₃(s) __ ⇌ ___ 2Al³⁺(aq) ___ + ___ 3SO₄²⁻(aq)
At eqm: _____ ---- _________ 2 × 1.81 × 10⁻⁵ M ___ 3 × 1.81 × 10⁻⁵ M

Solubility product, Ksp
= [Al³⁺]² [SO₄²⁻]³
= (2 × 1.81 × 10⁻⁵)² × (3 × 1.81 × 10⁻⁵)³
= 2.1 × 10⁻²²

(The calculations is based on the data given in the question. Actually, Al₂(SO₄)₃ is soluble in water with solubility 364 g/L at 20°C.)