Question

Systematic Treatment of Equilibrium:

Determine the pH of a 0.10M formic acid solution

Determine the pH of a 0.10M acetic acid solution

Determine the pH of a 0.10M carbonic acid solution

Determine the molar solubility of magnesium hydroxide in water at 25°C

Determine the molar solubility of calcium oxalate in a solution buffered to a pH of 4.00 at 25°C

Determine the molar solubility of calcium oxalate in water at 25°C

Answer 1

1. Formic acid is HCOOH. Its dissociation constant is 1.8 × 10^-4

The concentration of H⁺ ion in 0.1 M HCOOH is: ( Ka × [HCOOH])^1/2 = (1.8 ×10^-4 × 0.1)^1/2 M = 0.00424 M

pH = - log [H⁺] = - log (0.00424) = 2.37

2. Acetic acid is CH₃COOH . Its dissociation constant is 1.8 ×10^-5

Concentration of H⁺ ion in 0.1 M acetic acid us:

(Ka×[CH3COOH ])^1/2 = (1.8 ×10^-5×0.1)^1/2 = 0.00134 M

pH = - log [H⁺] = - log (0.00134) = 2.87

3 . The first acid dissociation constant of carbonic acid is 4.5 ×10^-7

So; [H⁺] = (0.1 ×4.5 ×10^-7) ^1/2 = 0.000212 M

pH = -log (0.000212) = 3.67

4. Magnesium hydroxide hydrolyses as:

Mg (OH)₂ (aq) = Mg⁺² (aq) + 2OH^- (aq)

Ksp = [Mg⁺²] × [OH^-]²

^{If the molar solubility of Mg (OH)₂ is s ththen;}

[Mg⁺²] = s and [OH-] = 2s

So; s × (2s)² = Ksp = 1.8 ×10^-11

4s³ = 1.8 ×10^-11

^{so; s = 0.000165 M}

^{molar solubility of magnesium hydrioxide is 0.000165 M.}