Question

The hydronium ion concentration of an aqueous solution of 0.45 M phenol (a weak acid), C₆H₅OH, is

[H₃O⁺] =  M

Answer 1

Sol :-

ICE table is :

..........................C₆H₅OH (aq)... .+... H₂O (l)---------------> C₆H₅O^-(aq) ................+.............H₃O⁺(aq)

Initial (I).............0.45 M.................................................0.0 M..........................................0.0 M

Change (C)...........-y .......................................................+y.................................................+y

Equilibrium (E)....(0.45-y) M...........................................y M...............................................y M

Expression of K_a is :

K_a = [C₆H₅O^- ].[H₃O⁺] / [C₆H₅OH]

1.3 x 10^-10 = y²/(0.45-y)

As y <<<0.45, so neglect y as compare to 0.45

y² = (0.45)(1.3 x 10^-10)

y = 7.65 x 10^-6

So,

[H₃O⁺] = 7.65 x 10^-6 M