Experiment 56

Objective

To identify the presence of lead ions in a sample by observing the formation of lead chromate.

Introduction

Lead salts react with potassium chromate to produce a yellow precipitate of lead chromate (PbCrO₄), which is soluble in dilute nitric acid, confirming the presence of lead ions.

Reaction:

Pb(NO3)2 + K2CrO4 → PbCrO4 ↓ + 2KNO3

Materials

Chemicals

·       Lead nitrate (Pb(NO₃)₂)

·       Potassium chromate (K₂CrO₄)

·       Distilled water

Apparatus

·       Test tube

·       Test tube holder

·       Bunsen burner

Reagents

·       3–4 ml of the lead sample in a test tube

Procedure

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

2.    Heat the test tube in a hot water bath.

3.    Add 7–8 ml of potassium chromate solution to the sample.

4.    Observe and record any changes.

Observation

A yellow precipitate forms upon the addition of potassium chromate, indicating the presence of lead ions.

Questions

1.    What is potassium chromate?

2.    What is a lead salt?

3.    How is a lead salt identified?

4.    What reagent is used in lead salt identification?