Introduction

The detection and identification of hydroxyl groups in organic compounds is a fundamental skill in organic chemistry. This article explores the main chemical tests used to identify and distinguish between different types of alcohols, including the sodium metal test, Lucas test, and various oxidation tests.

Sodium Metal Test

The sodium metal test is a qualitative method that identifies the presence of hydroxyl groups through the reaction between sodium metal and alcohols. When sodium reacts with an alcohol, it produces hydrogen gas and an alkoxide salt:

$2ROH_{(l)} + 2Na_{(s)} \rightarrow 2RONa_{(aq)} + H_2{(g)}$

The Pop Test

To confirm the presence of hydrogen gas, a lit splint is introduced to the test tube, resulting in a characteristic "pop" sound due to the reaction:

$2H_2{(g)} + O_2{(g)} \rightarrow 2H_2O_{(l)}$

Advantages and Limitations

Oxidation Tests

Understanding Oxidation States

Carbon oxidation states in organic molecules follow these rules:

Dichromate Oxidation Test

The acidified dichromate test uses Cr₂O₇²⁻/H⁺ to differentiate alcohols:

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

Results:

Permanganate Oxidation Test

The permanganate test (MnO₄⁻/H⁺) follows the reaction:

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

Results:

Lucas Test

The Lucas test uses concentrated HCl and ZnCl₂ to distinguish between different types of alcohols based on reaction rates:

[Insert Image 5: Lucas Test Results]

Results:

Silver Mirror Test (Tollen's Reagent)

The Tollen's test involves the reduction of silver ions:

$\text{Ag(NH}_3)_2^+\text{(aq)} + \text{e}^- \rightarrow \text{Ag}\text{(s)} + 2\text{NH}_3\text{(aq)}$

Results: