Titration of Nitrous Acid with Sodium Hydroxide

[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.

 

[Gokul43201]

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.

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?

 

[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?

 

[Gokul43201]

Correct. Now, what's the next step?

 

[rcrx]

Find the new Molarity of either substance?