JEE Main · 2019 · 12 Apr 2019 · Shift 2 · Equilibrium

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The decreasing order of electrical conductivity of the following aqueous solutions is:
0.1 M Formic acid (a)
0.1 M Acetic acid (b)
0.1 M Benzoic acid (c)

(A) $a > c > b$ ✓ Correct
(B) $c > a > b$
(C)c $>$ b $>$ a
(D)a $>$ b $>$ c

Answer: (A)

Solution

Conductivity here follows the degree of ionisation, which tracks acid strength. Formic acid is the strongest (

K_{a} \approx 1.8 \times 1 0^{- 4}

), benzoic acid comes next (

K_{a} \approx 6.3 \times 1 0^{- 5}

), and acetic acid is the weakest (

K_{a} \approx 1.8 \times 1 0^{- 5}

). More ionisation means more ions and higher conductivity, so the order is formic

>

benzoic

>

acetic, i.e.

a > c > b

JEE Main · 2019 · 12 Apr 2019 · Shift 2 · Single correct option

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