Calculating titrations beyond stoichiometric point

[Ashley Chen]

In homework, 13.27 part e, it asks calculate the pH at each stage in the titration for the addition of 0.150M HCL to 25.0mL of 0.110M NaOH after the addition of 5.0mL of acid beyond stoichiometric point.

Why does the calculation only include [H30+]? I'm confused on the reasons to why the calculations are the way they are in the solution manual. can someone explain?

[Brandon Truong 2G]

Because at the stoichiometric point, all of the base has been neutralized by the acid and leaving behind only a salt and water. Since NaOH is a strong base and HCl are strong acids, the salts that are formed do not affect the pH. When you keep adding more acid, all you're doing is adding more H30+ since there is no more OH- to neutralize it.

[Alison Ou 14a]

My reply is attached as an image since it's easier to write equations down than to type them. Hope it helps!

[Pauline Tze 3B]

This was really helpful! Thank you Alison :)