Experiment 51

Objective

To identify the presence of formic acid in a sample using mercuric chloride as a reagent.

Introduction

Formic acid reacts with mercuric chloride (HgCl₂) to produce a series of color changes in the precipitate, indicating its presence. Initially, formic acid reduces mercuric chloride to mercurous chloride, a white precipitate, and further reduction results in metallic mercury, which appears as a gray precipitate.

Chemical Reactions:

1.    Formation of mercurous chloride (white precipitate):

HgCI2  +  HCOOH  →  CO2  +  HCI  +  Hg2CI2

2.    Formation of mercury (gray precipitate):

HCOOH  +  Hg2CI2   →  CO2  +  HCI  +  Hg

Materials

Chemicals

·       Formic acid

·       Mercuric chloride (HgCl₂)

Apparatus

·       Test tube

·       Test tube holder

·       Dropper

·       Bunsen burner

Preparation of Reagents

·       Place 5-6 mL of formic acid in a test tube.

·       Add 2-3 mL of mercuric chloride solution to the formic acid.

Procedure

1.    Place the formic acid sample in a test tube.

2.    Secure the test tube in a test tube holder.

3.    Add mercuric chloride (HgCl₂) solution to the test tube.

4.    Observe any color changes after 1-2 minutes.

Observation

·       A white precipitate (mercurous chloride) appears initially, followed by a gray precipitate (metallic mercury), indicating the presence of formic acid in the sample.

Questions

1.    Why is HgCl₂ used in this experiment?

2.    What color changes are observed during the reaction?

3.    Describe the process involved in the identification test for formic acid.