HELP! MEDAL AND FAN!!
A 22.2 mL sample of a 0.346 M aqueous nitrous acid solution is titrated with a 0.436 M aqueous potassium hydroxide solution. What is the pH at the start of the titration, before any potassium hydroxide has been added?

Question

anonymous · Answer

before any potassium hydroxide has been added, the nitrous acid HNO2 is 0.346 M
HNO2 <------> H+    +   NO2-
0.346M                0.346 M

pH= -log [H+]
u can calculate from it

gebooors · Answer

It is a weak acid, a dissociation constant Ka have to be used.

Ka = 7.2*10^-4. Approximation gives

[H+] = square root( Ka * c)