Introduction

Chemical tests are essential tools for identifying functional groups in organic compounds. This article examines specific tests to distinguish between aldehydes, ketones, and carboxylic acids.

Oxidation Tests for Aldehydes and Ketones

Dichromate Test

The acidified dichromate test (Cr₂O₇²⁻/H⁺) provides a reliable method to differentiate aldehydes from ketones. The reaction involves:

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

Key observations:

Permanganate Test

The acidified permanganate test (MnO₄⁻/H⁺) offers another method for identification. The reaction follows:

${MnO_4^- + 8H^+ + 5e^- -> Mn^{2+} + 4H_2O}$

Key observations:

Tests for Carboxylic Acids

pH Indicator Test

Carboxylic acids can be identified using pH indicators:

Note: Aldehydes and ketones give neutral solutions.

Carbonate Test

The sodium carbonate test provides a definitive identification method for carboxylic acids.

When Na₂CO₃ or NaHCO₃ is added:

The CO₂ produced can be confirmed using the limewater test:

${CO_2(g) + Ca(OH)_2(aq) -> CaCO_3(s) + H_2O(l)}$

A positive test shows the clear solution turning milky white.