# What is the pH after adding a base?

1. Nov 17, 2009

### megzb

This is my question:
When a 17.9 mL sample of a 0.493 M aqueous nitrous acid solution is titrated with a 0.476 M aqueous barium hydroxide solution, what is the pH after 13.9 mL of barium hydroxide have been added?
I'm not really sure how to start it?
I have the moles of the acids and the base.
[acid]=8.8247E-3
[base]=6.6164E-3
but after that I'm lost! Help would be greatly appreciated!

2. Nov 17, 2009

### Staff: Mentor

Classic buffer question. Assume neutralization went to completion, calculate concentrations of acid and conjugate base, use Henderson-Hasselbalch equation.

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3. Nov 17, 2009

### megzb

And how do I find the concentrations exactly?

4. Nov 17, 2009

### Staff: Mentor

Stoichiometry. You start with some amount of nitrous acid. You add some base. If neutralization went to completion, you are able to easily calculate amount of the acid left, and amount of conjugate base (product of the reaction) - this is just a limiting reagent question. You know amounts, you know the final volume - just plug and chug.

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methods

5. Nov 18, 2009

### Biophreak

The molarity of your acid/base is given. Molarity = Moles/Liter IS your concentration.

6. Nov 18, 2009

### Staff: Mentor

Note: in case base is in excess all acid was neutralized, and it is just a limiting reagent question.

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