JEE Main 2026 — Ionic Equilibrium Question with Solution
JEE Main 2026 (28 January Shift 1)
Question
Consider the dissociation equilibrium of the following weak acid
If the pKa of the acid is 4, then the pH of 10 mMHA solution is .(Nearest integer)
[Given: The degree of dissociation can be neglected with respect to unity]
If the pKa of the acid is 4, then the pH of 10 mMHA solution is .(Nearest integer)
[Given: The degree of dissociation can be neglected with respect to unity]
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Show full solutionCorrect answer: 3
Correct answer
3
Step-by-step explanation
For the weak acid dissociation with pKa = 4
We have Ka = 10⁻⁴.
For a 10 mM (0.01 M) solution where the degree of dissociation is negligible with respect to unity, the concentration of HA remains approximately 0.01 M.
The equilibrium expression gives
Substituting: , which yields , so M.
Therefore, pH = .
We have Ka = 10⁻⁴.
For a 10 mM (0.01 M) solution where the degree of dissociation is negligible with respect to unity, the concentration of HA remains approximately 0.01 M.
The equilibrium expression gives
Substituting: , which yields , so M.
Therefore, pH = .
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This is a previous-year question from JEE Main 2026, covering the Ionic Equilibrium chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.