Titration ph

[Cloud]

Titrant

[HNO₂]= 0.10 mol/dm3
v= 25ml = 0.025 dm3

+

Analyte

[NaOH]= 0.125 mol/dm3
v= 20ml = 0.02 dm3

Question is: What is the ph after adding a volume 10ml of titrant?
I know the answer is ph= 4,3

I'm not allowed to use Henderson Hasselbach equation.
This is the only type of titration ph calculation i don't know how to do. When you add a certain volume of the titrant and one of them not being strong (the acid in this case).

Hope you can help me with the calculation or at least the steps so that I can try it and confirm.
Thanks

[Vitalii]

Titrant

[HNO₂]= 0.10 mol/dm3
v= 25ml = 0.025 dm3

+

Analyte

[NaOH]= 0.125 mol/dm3
v= 20ml = 0.02 dm3

Question is: What is the ph after adding a volume 10ml of titrant?
I know the answer is ph= 4,3

I'm not allowed to use Henderson Hasselbach equation.
This is the only type of titration ph calculation i don't know how to do. When you add a certain volume of the titrant and one of them not being strong (the acid in this case).

Hope you can help me with the calculation or at least the steps so that I can try it and confirm.
Thanks

To answer this question you must know Ka of HNO₂.
By defenition:
Ka = [H+]* [NO₂-] / [HNO₂]
Then calculate the concentrations of NO₂- and HNO₂ after the addition of the titrate. and express [H+] in terms of other known values:
[H+] = Ka * [HNO₂] / [NO₂-]
Hope this helps.