Oxidise 1‑propanol to propionic acid using potassium dichromate in acidic medium. Write the balanced equation and state the number of electrons transferred per mole of 1‑propanol.

easy 2 marks Class 12 · Chemistry · Aldehydes Ketones and Carboxylic Acids

Answer

12 electrons per mole of 1‑propanol

The correct answer is 12 electrons per mole of 1‑propanol — 5. Therefore, 12 electrons are transferred per mole of 1‑propanol.

Step-by-step solution

1. Write oxidation of 1‑propanol to propionic acid: $d i s pl a y s t y l ece C H 3 C H 2 C H 2 O H + 2 K 2 C r 2 O 7 + 8 H 2 S O 4 - > C H 3 C H 2 C O O H + 2 K 2 S O 4 + 4 C r 2 (S O 4) 3 + 9 H 2 O$
2. Count electrons: each $ce C r (V I)$ in $ce K 2 C r 2 O 7$ is reduced to $ce C r (I I I)$ , a gain of 3 e $^{-}$ per Cr atom.
3. Two $ce C r (V I)$ atoms are reduced in one $ce K 2 C r 2 O 7$ , so 6 e $^{-}$ per dichromate ion.
4. Two dichromate ions are used, giving 12 e $^{-}$ per mole of 1‑propanol.
5. Therefore, 12 electrons are transferred per mole of 1‑propanol.

Common mistake: Not accounting for all dichromate ions, leading to 6 e

^{-}

instead of 12.

Concept tested: Oxidation of alcohol to carboxylic acid