Ionic EquilibriumHard

Question

If the equilibrium constant for the reaction of weak acid HA with strong base is 109, then pH of 0.1 M Na A is

Options

A.5
B.9
C.7
D.8

Solution

HA + NaOH → NaA + H2O;   or   HA + OH- → A- + H2O
Keq. = 109 =    Also    HA ⇋ H+ + A-     Ka =
∴  or Ka = 109 × 10-14 = 10-5  Thus for
A- + H2O  ⇋  HA + OH
[OH-] = Ch = C = 10-5 M
∴  [H+]= 10- and pH = 9

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