Alcohol Classification Lab

Oxidation behavior with Acidified $K_2Cr_2O_7$

Reaction: $Cr_2O_7^{2-} \text{ (Orange)} \rightarrow Cr^{3+} \text{ (Green)}$
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Lab Manual: Aim, Theory & Procedure
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Aim

To distinguish between primary, secondary, and tertiary alcohols using acidified Potassium Dichromate based on their oxidation behavior.

Principle

Primary: Oxidized to aldehydes and carboxylic acids (Orange $\rightarrow$ Green).
Secondary: Oxidized to ketones (Orange $\rightarrow$ Green).
Tertiary: Resistant to oxidation (Remains Orange) due to lack of $\alpha$-hydrogen.

$Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$

Procedure

  1. Prepare Reagent: Add Dichromate and Acid to Tube 1, 2, and 3.
  2. Add Samples: Add Primary alcohol to Tube 1, Secondary to Tube 2, and Tertiary to Tube 3.
  3. Heating: Place tubes in the Water Bath at $70^\circ\text{C}$.
  4. Observe: Look for the orange-to-green color shift.

Reagent Bench

Dichromate
Acid
Primary
Secondary
Tertiary
TUBE 1
TUBE 2
TUBE 3

Heating Station ($70^\circ\text{C}$)

Predict Before You Heat

Which alcohol classes do you expect acidified K₂Cr₂O₇ to oxidise (orange → green)? Tick all that apply, then explain why.

Heating is locked until you predict.

Observation Log

Tube Class Result

Logic Monitor

Add Acid and Dichromate to the tubes, then select the alcohols to test.

⚠️ Safety — Alcohol Oxidation

Ready