Experiment 49

Objective

To identify the presence of ferric ions in a sample by observing the formation of a brown precipitate of ferric ferricyanide.

Introduction

Ferric salts react with potassium ferricyanide to produce a brown precipitate of ferric ferricyanide. This color change serves as a confirmatory test for the presence of ferric ions in the sample.

Reaction:

FeCl3 + K3[Fe(CN)6] → Fe[Fe(CN)6 ]↓+3KCl

Materials

Chemicals

·       Supplied sample containing ferric salt

·       Potassium ferricyanide (K₃[Fe(CN)₆])

·       Distilled water

Apparatus

·       Test tube

·       Test tube holder

·       Bunsen burner

Reagents

·       Dissolve 3.657 g of the supplied sample in 250 ml of distilled water.

·       Potassium ferricyanide solution prepared in a beaker.

Procedure

1.    Place 5–6 ml of the sample solution in a test tube.

2.    Add 3–4 ml of potassium ferricyanide solution to the test tube.

3.    Wait a few minutes for the reaction to complete.

4.    Observe any color change in the solution.

Observation

Upon adding potassium ferricyanide, a brown precipitate forms, indicating the presence of ferric ions.

Questions

1.    What is a ferric salt?

2.    What color forms when potassium ferricyanide is added?

3.    What is potassium ferricyanide?

4.    What happens during the ferric salt test?