The pKa of acetic acid, given its equilibrium dissociation constant (Ka) of 1.74 × 10-5 M, is 4.8 when rounded to one decimal place.

Calculation Steps

Acetic acid dissociates as CH₃COOH ⇌ CH₃COO⁻ + H⁺, where Ka = [CH₃COO⁻][H⁺]/[CH₃COOH].

pKa defines acid strength via the formula pKa = -log₁₀(Ka).

Substitute Ka: pKa = -log₁₀(1.74 × 10-5) = 4.759, which rounds to 4.8.

No Options Provided

This numerical question lacks multiple-choice options, so no alternatives require evaluation. Common distractors in similar CSIR NET problems include unrounded values (4.76 or 4.8 without rounding check) or errors like using log(Ka) instead of -log(Ka).

Introduction to pKa Calculation

In biochemistry and CSIR NET Life Sciences, determining the pKa of acetic acid from Ka 1.74 × 10-5 measures acid strength for buffers and enzyme kinetics. Ka, the equilibrium dissociation constant, quantifies weak acid ionization; pKa simplifies it logarithmically for practical use.

Step-by-Step Derivation

Formula: pKa = -log10(Ka)

Input: Ka = 1.74 × 10-5 M

Log Calculation: log(1.74 × 10-5) = log(1.74) + log(10-5) ≈ 0.240 – 5 = -4.760

pKa: -(-4.760) = 4.760 ≈ 4.8 (one decimal place)

This matches standard values near 4.76, adjusted for given Ka.

CSIR NET Relevance

Applications: pKa predicts ionization in buffers (Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA])) for protein stability, enzyme activity.

Common Errors:

  • Forgetting negative sign: Yields ~4.8 instead of 4.8? No—direct mistake gives positive log error.
  • Rounding prematurely: 4.76 vs. 4.8.
  • Ka misread: 1.8 × 10-5 gives 4.74.

Verification: Python confirms: import math; -math.log10(1.74e-5) → 4.759

Quick Reference Table

Parameter Value Notes
Ka (given) 1.74 × 10-5 M Equilibrium dissociation constant
pKa (calculated) 4.8 Rounded to one decimal
Standard pKa ~4.76 For Ka ≈ 1.8 × 10-5

Master this for CSIR NET acid-base equilibrium questions in biochemistry units.