Experiment 2: Ligand Substitution Reactions

Aim: to investigate the ligand substitution reactions of some transition metal ions.

You will use:

Cu2+ (aq) / Harmful /
Fe2+ (aq) / Harmful /
Fe3+ (aq) / Harmful /
Co2+ (aq) / Toxic /
NH3 (aq) / Irritant /
Concentrated HCl / Corrosive /

Reactions of transition metal ions with NH3

Method:

1.  Add 1cm3 of each transition metal ion to a clean test tube.

2.  Add a few drops of NH3 and record your observations.

3.  Add more NH3 slowly until no further change occurs. Record your observations in the table below.

Results:

A few drops of NH3 / Excess NH3
Cu2+ (aq)
Fe2+ (aq)
Fe3+ (aq)

Equations:

Write equations, including state symbols, for the reactions that have occurred when NH3 is added to Cu2+.

Reaction with a few drops of NH3:

…………………………………………………………………………………………………………………………………………………………..

Reaction with excess NH3:

…………………………………………………………………………………………………………………………………………………………..


Reactions of Cu2+

Method:

1.  Place 2 cm depth of water in a tube then add two spatula fulls of the anhydrous copper sulphate (note the colour) and mix thoroughly. Note any colour and temperature changes. Retain solution for number 3 below.

Observations:

…………………………………………………………………………………………………………………………………………………………..

Equation:

…………………………………………………………………………………………………………………………………………………………..

2.  Place 2 cm depth of conc HCl (CARE!) in a test tube and add 2 spatula fulls of anhydrous copper sulphate, stir with glass rod, note colour and temperature changes

Observations:

…………………………………………………………………………………………………………………………………………………………..

Equation:

…………………………………………………………………………………………………………………………………………………………..

A ligand is a molecule or ion which can donate a pair of electrons to the empty d orbitals of the copper ion to form a co-ordinate bond, making a complex ion.

3.  Place a few drops of the solution from 1. above into a clean test tube and slowly add excess conc. HCl (CARE!) and stir well. Note colour and temperature changes.

Observations:

…………………………………………………………………………………………………………………………………………………………..

Equation:

…………………………………………………………………………………………………………………………………………………………..


Reactions of Co2+

Method: Cobalt (II) reactions undergo similar reactions to Copper (II) ions.

1.  Place 1 cm depth of aqueous cobalt chloride solution in a test tube and slowly add excess conc HCl (CARE!) and stir. Note observations. Retain solution.

Observations:

…………………………………………………………………………………………………………………………………………………………..

Equation:

…………………………………………………………………………………………………………………………………………………………..

2.  Slowly add water to the solution from 1 above until the colour changes. Note observations. Retain solution.

Observations:

…………………………………………………………………………………………………………………………………………………………..

Equation:

…………………………………………………………………………………………………………………………………………………………..

3.  Gently warm the test tube from 2 above. Take CARE and do not boil! Note observations. Allow to cool then cool further under the tap. Note observations.

Observation 1:

…………………………………………………………………………………………………………………………………………………………..

Equation 1:

…………………………………………………………………………………………………………………………………………………………..

Observations 2:

…………………………………………………………………………………………………………………………………………………………..

Equation 2:

…………………………………………………………………………………………………………………………………………………………..

Use Le Chatelier’s principle to explain the observations you have made for the above reaction.

…………………………………………………………………………………………………………………………………………………………..

…………………………………………………………………………………………………………………………………………………………..

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