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Ionic Equilibrium question

2019 · 9 Apr · Shift 2 · Q21
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Ionic Equilibrium question

2019 · 9 Apr · Shift 2 · Q21

JEE MainChemistryIonic EquilibriumMCQ+4 / −1
In an acid-base titration, 0.1 M HCl solution was added to the NaOH solution of unknown strength. Which of the following correctly shows the change of pH of the titraction mixture in this experiment? JEE Main 2019 (Online) 9th April Evening Slot Chemistry - Ionic Equilibrium Question 91 English
  1. A
    (C)
  2. B
    (A)
  3. C
    (B)
  4. D
    (D)
View written solutionFree

Correct answer: B

  1. Identify the type of titration

We are adding 0.1 M HCl0.1\,\text{M HCl}0.1M HCl to a solution of NaOH of unknown concentration.

  • Initial solution: strong base (NaOH)(\text{NaOH})(NaOH)
  • Titrant added: strong acid (HCl)(\text{HCl})(HCl)

So this is a strong acid–strong base titration, with acid added to base.

  1. How does pH change during the titration?

Since the flask initially contains NaOH:

  • At the start, the solution is basic, so pH>7\text{pH} > 7pH>7.
  • As HCl is added, it neutralizes NaOH: HCl+NaOH→NaCl+H2O\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}HCl+NaOH→NaCl+H2​O
  • Therefore, the pH decreases gradually.
  • At the equivalence point, for a strong acid–strong base titration, pH=7\text{pH} = 7pH=7
  • After equivalence, excess HCl makes the solution acidic, so pH<7\text{pH} < 7pH<7.

Thus, the correct titration curve must:

  1. start at high pH,
  2. decrease as acid is added,
  3. show a sharp fall near equivalence,
  4. pass through pH=7\text{pH} = 7pH=7 at equivalence,
  5. then continue below 7.
  1. Match with the given graph labels

The options are encoded as:

  • A: (C)
  • B: (A)
  • C: (B)
  • D: (D)

The correct graph for strong acid added to strong base is graph (A). Therefore the correct option is:

B\boxed{\text{B}}B​

  1. Comparison with stored correct answer

Stored correct answer = B

My derived answer = B

So they agree.

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