Question

In a titration of nitrous acid with NaOH, the pH of the solution is 3.14 when the moles of HNO2 and the moles of NO2-- are equal. What is the Ka of nitrous acid?

Answer 1

Answer:

$Ka=3.98x10^{-4}$

Explanation:

Hello there!

In this case, since the modelling of titration problems can be approached via the Henderson-Hasselbach equation to set up a relationship between pH, pKa and the concentration of the acid and its conjugate base, we can write:

$pH=pKa+log(\frac{[NO_2^-]}{[HNO_2]} )$

Whereas the pH is given as 3.14 and the concentrations are the same, that is why the pH would be equal to the pKa as the logarithm gets 0 (log(1)=0); thus, we can calculate the Ka via:

$Ka=10^{-pKa}=10^{-3.14}\\\\Ka=3.98x10^{-4}$

Best regards!