pH and Ka
Should be able to work back from a pH value to a value of Ka. Generally simpler than calculating pH.
The pH of 0.500 M HNO2 is 1.827. What is Ka of HNO2?
[H3O+] = 10-1.827 = 0.0149 M
[NO2-] = [H3O+] = 0.0149 M
[HNO2] = 0.500 - 0.0149 = 0.485 M
Ka = (0.0149)2/0.485 = 4.58 x 10-4