Question

The ksp of beryllium hydroxide, be(oh)2, is 6.92 × 10-22. calculate the molar solubility of this compound.

Answer 1

When Be(OH)₂ dissolves it dissociates into the following ions
Be(OH)₂ --> Be²⁺ + 2OH⁻
molar solubility is the number of moles that dissolve in 1 L of solution
If the molar solubility of Be(OH)₂ is 'x', molar solubility of Be²⁺ and OH⁻ ions are x and 2x respectively.
ksp is solubility constant for Be(OH)₂
ksp = [Be²⁺][OH⁻]²
6.92 * 10⁻²² = [x][2x]²
4x³ = 6.92 * 10⁻²²
x³ = 1.73 * 10⁻²²
x = 5.57 * 10⁻⁸ mol/L
molar solubility of Be(OH)₂ is 5.57 * 10⁻⁸ mol/L