STANDARDChemistry-Acids and Bases
STANDARD Chemistry pH Calculations MCQ Question
Type: MCQ-numerical-Medium
Kₐ for CH₃COOH is 1.8 × 10⁻⁵ and K_b for NH₄OH is
A
7.005
B
4.75
C
7.0
D
Between 6 and 7
Correct Answer
Option C
Detailed Explanation
CH₃COONH₄ is a salt of weak acid (CH₃COOH) and weak base (NH₄OH). pH = 7 + 1/2 (pKₐ - pK_b). pKₐ = -log (1.8 × 10⁻⁵) = 4.74 and pK_b = -log (1.8 × 10⁻⁵) = 4.74. Therefore, pH = 7 + 1/2 (4.74 - 4.74) = 7.0.
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