JEE Main · 2025 · Shift-IeasyIEQ-080

An aqueous solution of HCl with pH 1.0 is diluted by adding equal volume of water (ignoring dissociation of water). The…

Ionic Equilibrium · Class 11 · JEE Main Previous Year Question

Question

An aqueous solution of HCl with pH 1.0 is diluted by adding equal volume of water (ignoring dissociation of water). The pH of HCl solution would (Given log2=0.30\log 2 = 0.30):

Options
  1. a

    reduce to 0.5

  2. b

    increase to 1.3

  3. c

    remain same

  4. d

    increase to 2

Correct Answerb

increase to 1.3

Detailed Solution

Step 1: Find initial concentration

pH=1.0[\ceH+]=101=0.1 M\text{pH} = 1.0 \Rightarrow [\ce{H+}] = 10^{-1} = 0.1\ \text{M}

Step 2: Effect of dilution

Adding equal volume of water → concentration becomes half:

[\ceH+]new=0.12=0.05 M[\ce{H+}]_{\text{new}} = \frac{0.1}{2} = 0.05\ \text{M}

Step 3: Calculate new pH

pH=log(0.05)=log(120)=log20\text{pH} = -\log(0.05) = -\log\left(\frac{1}{20}\right) = \log 20

=log(2×10)=log2+1=0.30+1=1.30= \log(2 \times 10) = \log 2 + 1 = 0.30 + 1 = 1.30

Answer: (b) increase to 1.3

Note: Dilution of an acid always increases pH (becomes less acidic).

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