Question

A 0.1 molar solution of nitrous acid is 7.1 percent ionised at equilibrium what is the
A. Concentration Hydrogen ion and ph
B. Ka value of nitrous acid
C. Concentration of hydroxide ion and poH

Answer 1

NOPE.
Percent ionization = 7.1%. Fraction ionized = 7.1/100 = 0.071 and (H^+) = 0.1 x 0.071 = 0.0071 M.Then pH = -log(H^+) = 2.15 is the correct answer for A.
........................HNO2 ==> H+ + NO2^-
I........................0.1 M.........0........0
C.....................-0.0071..0.0071...0.0071
E......................0.0929...0.0071...0.0071
Ka = (H^+)(NO2^-)/(HNO2) = (0.0071)(0.0071)/(0.0929) = 5.43 x 10^-4 M is the correct answer for B which is Ka.
For C remember (H^+)(OH^-) = Kw = 1E-14 so (OH^-) = 1E-14/0.0071 = 1.41E-12 M and pOH = 11.85.

Answer 2

A. The concentration of hydrogen ion is 0.071 M and the pH is 1.15.
B. The Ka value of nitrous acid is 6.3 x 10^-4.
C. The concentration of hydroxide ion is 0.0093 M and the pOH is 2.03.