chemistry question

Question

Calculate the pH for each of the cases in the titration of 35 mL of 0.130 M KOH(aq) with 0.130 M HBr(aq).

I already know the first four I'm stuck on the last two.

Before addition of any HBr: 13.11

After addition of 13.5 mL HBr: 12.62

After addition of 22.5 mL HBr: 12.29

After addition of 35.5 mL HBr: 7

After addition of 40.5 mL HBr:

After addition of 50 mL HBr:

Answer 1

Before doing the last 2, I think your answer to the 4th part is not correct because the pH would be 7 when EQUAL volumes of KOH and HBr were present. In the 4th part you have a slight excess of HBr so pH should be slightly acidic.

0.00455 moles KOH

0.00527 moles HBr

0.000715 moles HBr in excess

Final volume = 75.5 ml = 0.0755 L

[H+] = 0.000715 mol/0.0755 L = 0.00947 M

pH = 2.02

0.00455 moles KOH

0.0065 moles HBr

0.00195 moles HBr in excess

Final volume = 85 ml = 0.085 L

[H+] = 0.00195 mol/0.085 L = 0.0233 M

pH = 1.63