when BaSO₄ dissolves in water it dissociates as follows;
BaSO₄ ---> Ba²⁺ + SO₄²⁻
molar solubility of compound is the amount of moles that can be dissolved in 1 L solution
if molar solubility of BaSO₄ is x then molar solubility of Ba²⁺ is x and SO₄²⁻ is x.
the formula for solubility product constant - ksp is as follows
ksp = [Ba²⁺][SO₄²⁻]
ksp = (x)(x)
ksp = x²
and ksp = 1 x 10⁻¹⁰
therefore
x² = 1 x 10⁻¹⁰
x = 1 x 10⁻⁵ M
the molar solubility of BaSO₄ is 1 x 10⁻⁵ M
