The Relative Strengths of Oxidising Agents

 In this investigation you will consider the following oxidising agents or oxidants.

 

Cl2 (aq), I2 (aq), Fe3+ (aq), Br2 (aq), MnO4- (aq), S4062- (aq)

 

The half equations for their action as oxidants are:

Cl2 (aq)  +  2e-                                  2Cl- (aq)

 

I2 (aq)  +  2e-                                    2I- (aq)                                

 

Fe3+ (aq)  +  e-                                  Fe2+ (aq)                          

 

Br2 (aq)  +  2e-                                  2Br- (aq)                                  

 

MnO4- (aq) +  8H+  +  5e-                   Mn2+ (aq)  +  4H2O

                                      

S4062- (aq)  +  2e-                                  2S2O32- (aq)                                                              

 

Use these half- equations to write ionic equations for the reactions below.

 

The aim of the exercise is to place the six oxidising agents in order of their oxidising power, putting the strongest first.

INSTRUCTIONS :Use about 1cm3 of each solution for each test.

Test

Observations, Deductions, Equations

1.  In separate test tubes add chlorine water to solutions of potassium bromide and potassium iodide.

Then add bromine water to potassium iodide solution. 

Carefully record all changes taking place.  Identify the products by adding one cm3 of 1,1,1 trichloroethane and shaking.

(In this solvent: chlorine is pale green, bromine orange/brown and iodine violet.)

Write ionic equations for the reactions and place the halogens in order of their relative oxidising power

 

2. Add a little bromine water to iron(II) ions and investigate whether the iron has been oxidised.

(Iron(III) gives a blood red colour with potassium thiocyanate solution

Record your observations and write an

ionic equation.

Which is the strongest oxidising agent

bromine or iron(II)?

 

3.     Place about 0.5 cm3 of potassium bromide in a test tube and add an equal volume of dilute sulphuric acid. 

Now add a few drops of potassium manganate(VII) solution and record the result. 

Identify the coloured product using TCE.  Write a balanced ionic equation consistent with your observations.  Put both these substances in order of strength as oxidants.

 

 

 

 

4. Predict whether manganate(VII) will oxidise iron(II) or whether iron(III) will oxidise manganese(II).

State how you would test your results experimentally. 

Test your predictions. 

Record your result and write a balanced ionic equation.

 

 

5.    Add iodine solution, drop by drop to sodium thiosulphate solution. 

Describe your results and write an equation. 

Which is the stronger oxidant?

 

 

 

6.    Working in a fume cupboard and wearing safety glasses, add a spatula measure of solid potassium manganate(VII) to about 1 cm3 of conc. hydrochloric acid. 

Identify the gas produced by

(i)    very carefully sniffing it and

(ii)   its effect on moist blue litmus paper. 

Write an ionic equation for the reaction.  Which is the stronger oxidant?

 

 

 

7.  Look back over all your results and piece together the order of strength of all the oxidants used.