Calculate [H3O+]

0.100 M NaNO2 and 5.00×10−2 M HNO2

so there's no Ka value for NaNO2, it can be ignored

5.6x10^-4 = x^2 / 5.00x10^-2

x = 5.3x10^-3

the answer is incorrect why? Thanks

1 answer

A mixture of a weak acide (HNO2) and its salt (NaNO2) is a buffer solution and you should be using the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid). NaNO2 is the base and HNO2 is the acid.
Find pH and convert to H3O^+.