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P Block Elements question

2023 · 25 Jan · Shift 2 · Q13
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P Block Elements question

2023 · 25 Jan · Shift 2 · Q13

JEE MainChemistryP Block ElementsMCQ+4 / −1
Potassium dichromate acts as a strong oxidizing agent in acidic solution. During this process, the oxidation state changes from :
  1. A
    + 2 to + 1
  2. B
    + 6 to + 2
  3. C
    + 6 to + 3
  4. D
    + 3 to + 1
View written solutionFree

Correct answer: C

  1. Identify the oxidizing species in potassium dichromate

    Potassium dichromate is K2Cr2O7\mathrm{K_2Cr_2O_7}K2​Cr2​O7​.

    The oxidation state of chromium in Cr2O72−\mathrm{Cr_2O_7^{2-}}Cr2​O72−​ is found as: 2x+7(−2)=−22x + 7(-2) = -22x+7(−2)=−2 2x−14=−22x - 14 = -22x−14=−2 2x=122x = 122x=12 x=+6x = +6x=+6

    So, chromium is initially in the oxidation state +6+6+6.

  2. Reduction in acidic medium

    In acidic solution, dichromate acts as an oxidizing agent and gets reduced to Cr3+\mathrm{Cr^{3+}}Cr3+: Cr2O72−+14H++6e−→2Cr3++7H2O\mathrm{Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O}Cr2​O72−​+14H++6e−→2Cr3++7H2​O

    Thus, chromium changes from +6+6+6 to +3+3+3.

  3. Check the options

    • A: +2+2+2 to +1+1+1 — incorrect
    • B: +6+6+6 to +2+2+2 — incorrect
    • C: +6+6+6 to +3+3+3 — correct
    • D: +3+3+3 to +1+1+1 — incorrect

  4. Final answer

    Potassium dichromate in acidic medium undergoes reduction of chromium from: +6→+3+6 \to +3+6→+3

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