Ionic EquilibriumHard

Question

What is the pH of 10−7 M-HCl solution at 25o C?

Options

A.7.0
B.6.70
C.6.62
D.6.79

Solution

As the acid is very dilute, the contribution of water should be taken. Let H2O dissociates only upto xM in presence of HCl.

H2O $\rightleftharpoons$ H+ + OH–

Equilibrium (x + 10–7) M x M

Now, [H+][OH–] = Kw ⇒ (x + 10–7) ⋅ x = 10–14

⇒ x = 6.18 × 10–8

∴ [H+] = (x + 10–7) M = 1.618 × 10–7 M

⇒ PH = 6.79

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