Experiment 50

Objective

To identify the presence of ferrous ions in a sample by observing the formation of a blue precipitate of potassium ferrous ferricyanide.

Introduction

Ferrous salts react with potassium ferricyanide to form an insoluble blue precipitate of potassium ferrous ferricyanide, which indicates the presence of ferrous ions.

Reaction:

FeSO4 + K3[Fe(CN)6] → KFe[Fe(CN)6] ↓ + K2SO4

Materials

Chemicals

·       Supplied sample containing ferrous 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

A blue precipitate forms upon the addition of potassium ferricyanide, indicating the presence of ferrous ions.

Questions

1.    What is a ferrous salt?

2.    What color forms when potassium ferricyanide is added?

3.    What is potassium ferricyanide?

4.    What reaction occurs during the ferrous salt test?