How many mmoles of HCl must be added to 100 mL of a 0.100 M solution of methylamine (pK_b = 3.36)to give a buffer having a pH of 10.00?

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Quizplus · Accepted Answer

To form a buffer with pH 10.00 using methylamine (a weak base), we use the Henderson-Hasselbalch equation: pH = pKa + log([base]/[acid]). First, calculate pKa from pKb: pKa = 14 - 3.36 = 10.64. Then, set up the equation: 10.00 = 10.64 + log([base]/[acid]). Solving gives [base]/[acid] = 0.229. Initially, there are 10 mmoles of methylamine (0.100 M * 100 mL). Let x be the mmoles of HCl added, then [base] = 10 - x and [acid] = x. Solving 0.229 = (10-x)/x gives x ≈ 8.1 mmoles.

How Many Mmoles of HCl Must Be Added to 100