Question

Write a balanced equation for the oxidation of cyclopentanol with potassium dichromate in the presence of sulfuric acid. Use half-cell method.

Answer 1

cyclo pentanone will get oxidised and give the cyclopentanone

reduction hal reaction

reduction half reaction

from the above reaction it is clear that Cr under go reduction

Cr₂O₇^2- ------> 2 Cr³⁺

Cr₂O₇^2- ------> 2 Cr³⁺ + 7 H₂O

14 H⁺ + Cr₂O₇^2- ------>   2 Cr³⁺ + 7 H₂O

14 H⁺ + Cr₂O₇^2- + 6 e^- ------>   2 Cr³⁺ + 7 H₂O

oxidation half reaction

C₅H₁₀O ------>   C₅H₈O

C₅H₁₀O  ------>   C₅H₈O + 2H⁺

C₅H₁₀O  ------>   C₅H₈O + 2H⁺ + 2e^-

now add the both euations

14 H⁺ + Cr₂O₇^2- + 6 e^- ------>   2 Cr³⁺ + 7 H₂O

C₅H₁₀O ------>   C₅H₈O + 2H⁺ + 2e^-

in order to get equate the electrons second euation we have to multyply with 3

3C₅H₁₀O ------>   3C₅H₈O + 6H⁺ + 6e^-

now add both euations

14 H⁺ + Cr₂O₇^2- + 6 e^- ------>   2 Cr³⁺ + 7 H₂O

3C₅H₁₀O ------>   3C₅H₈O + 6H⁺ + 6e^-

net Cr₂O₇^2- + 3C₅H₁₀O + 8H⁺ ------> 3C₅H₈O    + 2 Cr³⁺ + 7 H₂O