Answer:
10.57
Step-by-step explanation:
Step 1: Given and required data
- Concentration of NH₃ (Cb): 0.0075 M
- Basic dissociation constant for NH₃ (Kb): 1.8 × 10⁻⁵
Step 2: Write the basic dissociation reaction for NH₃
NH₃(aq) + H₂O(aq) ⇄ NH₄⁺(aq) + OH⁻(aq)
Step 3: Calculate the concentration of OH⁻
We will use the following expression.
[OH⁻] = √(Kb × Cb)
[OH⁻] = √(1.8 × 10⁻⁵ × 0.0075 M) = 3.7 × 10⁻⁴ M
Step 4: Calculate the concentration of H⁺
We will use the water ion product.
Kw = 1.0 × 10⁻¹⁴ = [H⁺] × [OH⁻]
[H⁺] = 1.0 × 10⁻¹⁴/3.7 × 10⁻⁴ = 2.7 × 10⁻¹¹ M
Step 5: Calculate the pH of the solution
We will use the definition of pH.
pH = -log [H⁺] = -log 2.7 × 10⁻¹¹ = 10.57