1. Understand the Dissociation:

Calcium hydroxide (Ca(OH)₂) is a strong base. It completely dissociates in water:

Ca(OH)₂ (aq) → Ca²⁺ (aq) + 2OH⁻ (aq)

This means that for every 1 mole of Ca(OH)₂ that dissolves, you get 2 moles of hydroxide ions (OH⁻).

2. Calculate the Hydroxide Ion Concentration:

* Since the concentration of Ca(OH)₂ is 0.15 M, the concentration of OH⁻ ions is twice that: 0.15 M * 2 = 0.30 M

3. Calculate the pOH:

pOH is the negative logarithm of the hydroxide ion concentration:

pOH = -log[OH⁻] = -log(0.30) ≈ 0.52

4. Calculate the pH:

The pH and pOH are related by the following equation:

pH + pOH = 14

Therefore:

pH = 14 - pOH = 14 - 0.52 ≈ 13.48

Therefore, the pH of a 0.15 M calcium hydroxide solution is approximately 13.48.