What is the solubility in moles/liter for magnesium hydroxide at 25 oC given a Ksp value of 1.1 x 10-11. Write using scientific notation and use 1 or 2 decimal places (even though this is strictly incorrect!)

S = 0.00014 moles / L = 1.4 * 10^-4 moles/L

Explanation:

Step 1: Data given

Temperature = 25.0 °C

Ksp = 1.1 * 10^-11

Step 2: The balanced equation

Mg (OH) 2 (s) ⇆ Mg^2 + (aq) + 2OH - (aq)

Step 3: Define Ksp

[Mg (OH) 2 = 1.11 * 10^-11 = S

[Mg^2+] = S

[OH-] = 2S

Ksp = [Mg^2+]*[OH-]²

Ksp = S * (2S) ²

1.1 * 10^-11 = 4S³

S³ = 2.75 * 10^-12

S = 0.00014 moles / L

1.40 * 10⁻⁴ M

Explanation:

Let's consider the solution of magnesium hydroxide.

Mg (OH) ₂ (s) = Mg²⁺ (aq) + 2 OH⁻ (aq)

We can relate the solubility (S) of the hydroxide with the solubility product (Ksp) using an ICE chart.

Mg (OH) ₂ (s) = Mg²⁺ (aq) + 2 OH⁻ (aq)

I 0 0

C + S + 2S

E S 2S

The solubility product is:

Ksp = [Mg²⁺] * [OH⁻]² = S * (2S) ² = 4 S³

S = ∛ (Ksp/4) = ∛ (1.1 * 10⁻¹¹/4)

S = 1.40 * 10⁻⁴ M