# Titration of Nitrous Acid with Sodium Hydroxide

1. Apr 16, 2010

### rcrx

A 25.0 ml sample of 0.150 M HNO2 is titrated with a 0.150 M NaOH solution. What is the pH at the equivalence point? The Ka of HNO2 is 4.50x10-4

What I can't get is the fact I don't know how much has already been titrated at the equivalence point. So it's difficult to know the total volume to find the new concentration.

The answer is supposed to be pH = 8.11, and I could guess that with the titration of a weak acid with a strong base that the pH will rise a bit. But I can't presume how to do this mathematically.

2. Apr 16, 2010

### Gokul43201

Staff Emeritus
If you are having trouble with this, you should take a step back ... and start at the definition of the equivalence point. What is the definition?

3. Apr 16, 2010

### rcrx

Both concentrations are in equal proportion and neither consumes the other. So that means there is 25.0 + 25.0 for a combined total of 50ml?

4. Apr 16, 2010

### Gokul43201

Staff Emeritus
Correct. Now, what's the next step?

5. Apr 18, 2010

### rcrx

Find the new Molarity of either substance?