Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine,C₂H₅NH₂,by 1.0 M perchloric acid,HClO₄.(pK_b for C₂H₅NH₂ = 3.25)

Question

Quizplus · Accepted Answer

At the equivalence point of the titration, moles of perchloric acid will be equal to moles of ethylamine, resulting in a solution containing only the conjugate acid, ethylammonium ion (C₂H₅NHC₂). The pKa of ethylammonium ion can be found using the formula pKa + pKb = 14, so pKa = 14 - 3.25 = 10.75. Since pH = pKa + log([conjugate base]/[acid]), at the equivalence point, [conjugate base] = [acid], and pH = pKa = 10.75. However, ethylammonium ion is a relatively weak acid, so its dissociation will be incomplete, and the pH will be slightly higher, around 5.5. Therefore, the correct answer is C.

Calculate the PH at the Equivalence Point for the Titration