Titration of 4500 mL of 0150 M Acetylsalicylic Acid with 015

Titration of 45.00 mL of 0.150 M Acetylsalicylic Acid with 0.150 M KOH

What is the pH of the initial solution?

pH at half equivalence point?

How much KOH volume added at half equivalence point

pH at equivalence point.

Solution

Let us take the weak acid , acetylsalicylic acid as HA

[HA] initial = 0.15M

pKa of acid = 3.5

1)The pH of initial solution is

pH = 1/2[pKa -logC]

=1/2[3.5 -log0.15]

=2.162

2) pHat half equialence

For the equivalence

mmoles ofacid = mmoles of base

45x0.15 = V x 0.15

Thus V = 45 mL  

Vlume of KOH at equivalence = 45mL

Volume of KOH at half equivalence = 45/2=22.5

HA + KOH -------------------------> KA + H2O

45x0.15 = 6.75 22.5x0.15= 3.375 0 0 initial mmoles

3.375 0 3.375 - at half equivalence

It is a buffer and its pH is calculated as

pH = pKa + log [salt]/[acid]

= 3.5 + log 3.375/3.375

=3.5

C) volume of KOH at half eqivalence = 22.5mL

D) pH at equivalence

HA + KOH -------------------------> KA + H2O

45x0.15 = 6.75 45x0.15= 6.75 0 0 initial mmoles

0 0 6.75 - at half equivalence

{salt] = 6.75/(45+45)

= 0.075M

The sal t is a salt of weak acid and strong base, so basic with pH>7

pH of salt = 1/2[pKw +pKa +logC]

=1/2[14+ 3.5+log 0.075]

=8.1875