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Ionic Equilibrium question

2022 · 28 Jul · Shift 2 · Q4
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Ionic Equilibrium question

2022 · 28 Jul · Shift 2 · Q4

JEE MainChemistryIonic EquilibriumMCQ+4 / −1
Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R Assertion A : Permanganate titrations are not performed in presence of hydrochloric acid. Reason R : Chlorine is formed as a consequence of oxidation of hydrochloric acid. In the light of the above statements, choose the correct answer from the options given below
  1. A
    Both A\mathrm{A}A and R\mathrm{R}R are true and R\mathrm{R}R is the correct explanation of A\mathrm{A}A
  2. B
    Both A\mathrm{A}A and R\mathrm{R}R are true but R\mathrm{R}R is NOT the correct explanation of A\mathrm{A}A
  3. C
    A\mathrm{A}A is true but R\mathrm{R}R is false
  4. D
    A\mathrm{A}A is false but R\mathrm{R}R is true
View written solutionFree

Correct answer: A

  1. Understand the assertion

    Assertion A: Permanganate titrations are not performed in presence of hydrochloric acid.

    This is true. In permanganate titrations, KMnO4\mathrm{KMnO_4}KMnO4​ acts as a strong oxidizing agent, especially in acidic medium. However, the acid used should generally be dilute sulfuric acid and not hydrochloric acid.

  2. Why is hydrochloric acid avoided?

    In acidic medium, permanganate oxidizes chloride ions from hydrochloric acid to chlorine gas.

    The relevant reaction is:

    2 MnO4−+16 H++10 Cl−→2 Mn2++8 H2O+5 Cl22\,\mathrm{MnO_4^-} + 16\,\mathrm{H^+} + 10\,\mathrm{Cl^-} \rightarrow 2\,\mathrm{Mn^{2+}} + 8\,\mathrm{H_2O} + 5\,\mathrm{Cl_2}2MnO4−​+16H++10Cl−→2Mn2++8H2​O+5Cl2​

    Because Cl−\mathrm{Cl^-}Cl− gets oxidized to Cl2\mathrm{Cl_2}Cl2​, part of the permanganate is consumed in this side reaction. Hence the titration becomes inaccurate.

  3. Check the reason

    Reason R: Chlorine is formed as a consequence of oxidation of hydrochloric acid.

    This is also true. More precisely, chloride ions from hydrochloric acid are oxidized to chlorine.

  4. Relation between A and R

    The reason directly explains why permanganate titrations are not carried out in presence of hydrochloric acid: formation of chlorine causes interference and wrong end point.

  5. Conclusion

    • Assertion A is true
    • Reason R is true
    • Reason R is the correct explanation of Assertion A

    Therefore, the correct option is A.

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