What is the pH of a buffer solution prepared by mixing 200 mL of 0.05 M aqueous ammonia with 100 mL of 0.01 M ammonium chloride? [Given: pK_b of NH_3 = 4.74 ]

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Correct answer: C. 10.26

Millimoles of NH_3 = 200 × 0.05 = 10 Millimoles of NH_4Cl = 100 × 0.01 = 1 Total volume = 300 mL [NH_3] = (10)/(300) M [NH_4^+] = (1)/(300) M Using the Henderson-Hasselbalch equation for a basic buffer: pOH = pK_b + ( ([NH_4^+])/([NH_3]) ) pOH = 4.74 + ( (1/300)/(10/300) ) pOH = 4.74 + (10^ -1 ) = 4.74 - 1 = 3.74 pH = 14 - pOH = 14 - 3.74 = 10.26 Answer: 10.26

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