Experiment 60

Objective

To identify the presence of nickel ions in a sample by observing the formation of a red precipitate of nickel dimethylglyoxime complex.

Introduction

Nickel ions (Ni²⁺) react with dimethylglyoxime in the presence of ammonium hydroxide to form a red precipitate of nickel dimethylglyoxime complex. This distinctive color change indicates the presence of nickel.

Reaction:

CH3​-C=NOH – CH3​-C=NOH + Ni2 + NH4​OH → [(CH3​-C=NOH – CH3​-C=NO)] Ni ↓ +                                                                                                                                                                                           2NH4 ​+ 2H2​O

Materials

Chemicals

·       Supplied sample containing nickel salt

·       Ammonium hydroxide (NH₄OH)

·       Dimethylglyoxime

Apparatus

·       Test tube

·       Test tube holder

·       Bunsen burner

Reagents

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

·       Ammonium hydroxide 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 ammonium hydroxide to the solution.

3.    Add twofold dimethylglyoxime to the test tube.

4.    Observe the reaction and note any changes in color.

Observation

A red precipitate forms in the solution, indicating the presence of nickel ions as a nickel dimethylglyoxime complex.

Questions

1.    What is dimethylglyoxime?

2.    How is the presence of nickel identified in this test?

3.    What color forms during the precipitation of nickel?