Phenol has an acid dissociation constant K_a = 1.3×10^-10 at 25°C. Calculate its pK_a.

Phenol has an acid dissociation constant $K_{a} = 1.3 \times 1 0^{- 10}$ at 25°C. Calculate its p $K_{a}$ .

easy 1 mark Class 12 · Chemistry · Alcohols Phenols and Ethers

Answer

9.89

The correct answer is 9.89 — 3. Calculate: $p K_{a} \approx 9.89$ .

1. $p K_{a} = - lo g_{10} K_{a}$ .
2. Substitute $K_{a} = 1.3 \times 1 0^{- 10}$ : $p K_{a} = - lo g_{10} (1.3 \times 1 0^{- 10})$ .
3. Calculate: $p K_{a} \approx 9.89$ .

Common mistake: Using

l o g_{10} (K_{a})

instead of

- lo g_{10} (K_{a})

Concept tested: Acid dissociation constant of phenol