Q. A buffer solution is prepared in which the concentration of NH₃ is 0.30 M and the concentration of NH₄⁺ is 0.20 M. If the equilibrium constant, Kb for NH₃ equals 1.8 × 10⁻⁵, what is the pH of this solution?

A) 8.73
B) 9.08
C) 9.43
D) 11.72
Explanation

[Solution from source] pKb = −log(1.8 × 10⁻⁵) = 4.74. pOH = pKb + log([NH₄⁺]/[NH₃]) = 4.74 + log(0.20/0.30) = 4.74 − 0.18 = 4.57, so pH = 14 − 4.57 = 9.43. Swapping the ratio gives pOH 4.92 and pH 9.08, the trap. Answer (3).

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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