experment1 Electron Transfer (Redox) Reactions
1. Comparison of Br2/Brâ and Fe3+/Fe2+ Couples
Oxidant-reductant pairs from these couples will he tested, i.e. Br2 with the reductant Fe2+ and
Brâ with the oxidant Fe3+. A reaction will occur in only one of these cases because of the
difference in electrode potential between the two couples.
To test whether reaction has occurred, SCNâ will be used as a probe for Fe3+, with which it
gives a red complex. Note that the air rapidly oxidises Fe2+, so that a faint pink colour is often
obtained when SCNâ is added to Fe2+.
Solutions containing Fe2+ or Fe3+ tend to decompose (although in different ways); both are
stabilised by H+. The iron(II) solution provided is freshly prepared 0.1 M (NH4)2Fe(SO4)2 / 2
M H2SO4.
To 5 drops of the 0.1 M iron(II) solution in a semi-micro tube add 10 drops of 0.1 M KBr and
stir. Place 1 drop of the mixture on a white tile, and test for Fe3+ by adding 1 drop 0.1 M
KSCN. A strong red colour indicates Fe3+.
Repeat using 5 drops of the 0.1 M iron(III) solution and adding 10 drops of 0.1 M KBr.
Repeat using 5 drops of the 0.1 M iron(II) solution and adding 10 drops of 0.1 M Br2.
Repeat using 5 drops of the 0.1 M iron(III) solution and adding 10 drops of 0.1 M Br2.
2.Use of the Br2/Brâ and Fe3+/Fe2+ Couples in an Electrochemical Cell
You are supplied with a pair of carbon rods joined by copper wire. Place two 100 mL beakers
side by side.
In one put 50 mL of the iron(II) solution and 1 mL of 0.1 M KSCN solution. In the other
beaker put 25 mL of 0.2 M Br2 solution and 25 mL of 4 M HCl.
Correct any difference in level between the solutions in the two beakers by adding water to
one. Fold an 11 cm filter paper into a strip about 1 cm wide. Bend the strip in the middle,
moisten with a little 4 M HCl, then insert the strip so that it links the two solutions. Insert one
carbon rod into each solution, then allow to stand undisturbed for 30 minutes while
proceeding with Experiment 3. Carefully observe the apparatus at intervals and record any
change that occurs.
3. Comparison of the Fe3+/Fe2+ and Sn4+/Sn2+ Couples
In this experiment the additional sources of ions are:
tin(IV) ion 0.1 M SnCl4/1 M HCl
tin(II) ion 0.1 M SnCl2/1 M HCl
(Both Sn2+ and Sn4+ solutions are stabilised by H+.)
To 5 drops of the 0.1 M iron(II) solution in a semi-micro tube add 10 drops of the appropriate
0.1 M tin solution and stir. Place 1 drop of the mixture on a white tile, and test for Fe3+.
Record the results.
Similarly, test the 0.1 M iron(III) solution with an excess of the appropriate 0.1 M tin
solution.
You have now enough information to state whether the standard electrode potential of the
Fe3+/Fe2+ couple is more positive or less positive than that of the Sn4+/Sn2+ couple.
please answer following questions
1.Comparison of Br2/Brâ and Fe3+/Fe2+ couples
Complete the following table.
