A 50.00-mL solution of 0.0350 M ethylamine (K_b = 5.6 × 10^-4)is titrated with a 0.0135 M solution of hydrochloric acid as the titrant.What is the pH at the equivalence point? (K_w = 1.0 × 10^-14) A) 10.75 B) 6.38 C) 2.63 D) 3.25 E) 7.62

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Quizplus · Accepted Answer

At the equivalence point in the titration of a weak base with a strong acid, the solution contains the conjugate acid of the weak base. The pH is determined by the hydrolysis of this conjugate acid. The Kb for ethylamine can be calculated from its given pKb (5.6 × 10^-4), and then the Ka for the conjugate acid can be found using the relation Ka*Kb = Kw, where Kw is the ion product of water (1.0 × 10^-14). Once Ka is known, the concentration of the conjugate acid at the equivalence point can be used to calculate the pH, which typically falls below 7 for a weak base-strong acid titration, making 6.38 the correct answer.

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