Experiment 67

Objective

To identify primary, secondary, and tertiary alcohols in the laboratory using Lucas reagent.

Introduction

Lucas reagent, a mixture of zinc chloride (ZnCl₂) and hydrochloric acid (HCl), reacts differently with primary, secondary, and tertiary alcohols. Tertiary alcohols react almost immediately, forming a white precipitate, while secondary alcohols form a precipitate within 5-10 minutes. Primary alcohols react very slowly, often requiring heat.

Reaction Overview

·       Tertiary Alcohol: Rapid white precipitate

·       Secondary Alcohol: Precipitate after 5-10 minutes

·       Primary Alcohol: Precipitate forms only with heating

Materials

Chemicals

·       Primary alcohol

·       Secondary alcohol

·       Tertiary alcohol

·       Zinc chloride (ZnCl₂)

·       Hydrochloric acid (HCl)

Apparatus

·       Test tubes (one for each type of alcohol)

·       Test tube holders

·       Bunsen burner

·       White paper for color observation

Reagents

·       Add 2-5 mL of each alcohol to separate test tubes and 3-5 drops of Lucas reagent to each.

Procedure

1.    Preparation of Test Tubes

o   Place 2-5 mL of each type of alcohol (primary, secondary, and tertiary) in separate test tubes.

2.    Addition of Lucas Reagent

o   Add 3-5 drops of Lucas reagent (ZnCl₂ in HCl) to each test tube.

3.    Observation

o   Observe each test tube for white precipitate formation:

§  Tertiary alcohol: White precipitate forms almost immediately.

§  Secondary alcohol: White precipitate forms after 5-6 minutes.

§  Primary alcohol: Requires heating with a Bunsen burner to form a white precipitate.

Observation

Tertiary alcohols react quickly to form a white precipitate, secondary alcohols produce a precipitate after a delay, and primary alcohols require heating for precipitate formation.

Questions

1.    What are primary, secondary, and tertiary alcohols?

2.    What is Lucas reagent?

3.    How do different types of alcohols react with Lucas reagent?