Experiment 46

Objective

To identify the presence of ethanal in a carbonyl compound using Fehling's solution, iodine, and NaOH.

Introduction

Ethanal can be identified by its reaction with Fehling's solution and then with iodine and NaOH. The two reactions indicate ethanal by producing distinct precipitates. Initially, the ethanal reduces Fehling's solution to form a red precipitate of Cu₂O (copper(I) oxide). Subsequently, reacting with iodine and NaOH produces a yellow iodoform precipitate.

Reactions:

1.    With Fehling's Solution:

CH3CHO + Cu(OH)2  ​→ CH3​COONa + Cu2​O (red ppt) +H2​O

2.    With Iodine and NaOH:

CH3​CHO + I2 ​+ NaOH → CHI3​(yellow ppt) + HCOONa + NaI + H2​O

Materials

Chemicals

●      Ethanal

●      Cu(OH)₂ (for Fehling's solution)

●      NaOH

●      Iodine (I₂)

Apparatus

●      Test tube

●      Test tube holder

●      Bunsen burner

Reagents

●      5–6 ml of ethanal solution

●      2–3 ml of Fehling's solution

●      Iodine and NaOH for the second reaction

Procedure

1.    Place the ethanal sample in a test tube.

2.    Add 2–3 ml of Fehling's solution.

3.    Heat the test tube for 5–6 minutes using a Bunsen burner.

4.    After observing the red precipitate, add iodine and NaOH to the test tube.

5.    Heat the solution again until a yellow precipitate forms, then stop heating.

Observation

A red precipitate of Cu₂O forms in the first reaction, and a yellow iodoform precipitate appears in the second reaction, confirming the presence of ethanal.

Questions

1.    What is Fehling's solution?

2.    What is iodoform?

3.    How is ethanal identified in this test?

4.    What occurs during the reaction between ethanal and Fehling's solution?