NCERT Class XI Chemistry Equilibrium Solutions

Question : 44

Total: 73

The ionization constant of phenol is 1.0 × 10–10. What is the concentration of phenolate ion in 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01M in sodium phenolate?

Solution:

C6H5OH ⇌ C6H5O−+H+

Initial‌concentration	0.05M	0	0
After‌dissociation	0.05−x	x	x

∴ K‌a =

x×x

0.05−x

= 1.0 × 10−10 (Given)
or

0.05

= 1.0 × 10−10 [Since 0.05 - x ≈ 0.05]
or x2 = 5 × 10−12 or, x = 2.33 × 10−6M
In presence of 0.01 M C6H5ONa, suppose y is the amount of phenol dissociated, then at equilibrium
[C6H5OH] = 0.05 – y ≈ 0.05 M
[C6H5O–] = 0.01 + y ≈ 0.01 M, [H+] = y M
∴ Ka =

(0.01)(y)

0.05

= 1.0 × 1010 (Given) or y = 5 × 10−10
∴ α =

5×10−10

0.05

= 1 × 10−8

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