Calculate the pH at the equivalence point for the titration

Calculate the pH at the equivalence point for the titration of 0.240 M methylamine (CH3NH2) with 0.240 M HCI. The Kb of methylamine is 5.0x 104 Number pH-5.64

Solution

at equivalence point tital amine becomes salt.

[salt] = 0.240 / 2 = 0.12 M

equal volume of HCl required to reach equivalence point so concentration becomes half.

for salts of weak bases at equivalence point

pOH = 1/2 [pKw + pKb + log C]

pKb = - log Kb = - log [5.0 x 10^-4] = 3.30

pOH = 1/2 [14 + 3.30 + log 0.12]

pOH = 8.20

pH = 14 - 8.20

pH = 5.80