calculate the pH of a 1.94M solution of nitrous acid (HNO2 - ka = 4.5E-4).

Answer 1

Set up an ICE chart, something like the following:
............HNO2 ==> H^+ + NO2^-
initial....1.94M.....0.......0
change......-x.......+x.......+x
final......1.94-x.....x........x

Ka = (H^+)(NO2^-)/(HNO2)
Substitute from the ICE chart to the Ka expression, solve for x and convert to pH.

Answer 2

for .148M it is 2.00