Laboratory Activity 1B (Conversion of Iron(II) Ion, Fe2+ to Iron(III) Ion, Fe3+ and Vice Versa):
Aim: To study the conversion of iron(II) ion, Fe2+ to iron(III) ion, Fe3+ and vice versa.
Materials: 0.5 mol dm−3 of iron(II) sulphate, FeSO4 solution (freshly prepared), 0.5 mol dm−3 of iron(III) chloride, FeCl3 solution, bromine water, Br2 , zinc powder, Zn and 2.0 mol dm−3 of sodium hydroxide, NaOH solution.
Apparatus: Boiling tube, test tube, boiling tube holder, dropper, spatula, filter funnel, filter paper, Bunsen burner and test tube rack.
Procedure:
A. Conversion of iron(II) ion, Fe2+ to iron(III) ion, Fe3+
1. Pour 2 cm3 of 0.5 mol dm−3 of iron(II) sulphate, FeSO4 solution (freshly prepared) into a boiling tube held by a boiling tube holder as shown in Figure 1.5.
2. Using the dropper, add bromine water, Br2 while shaking the boiling tube until no further colour change can be observed.
3. Gently heat the mixture in the boiling tube.
4. Add sodium hydroxide, NaOH solution into the mixture to confirm the presence of iron(III) ion, Fe3+.
5. Record all observations.
B. Conversion of iron(III) ion, Fe3+ to iron(II) ion, Fe2+
1. Pour 2 cm3 of 0.5 mol dm−3 of iron(III) chloride, FeCl3 solution into a boiling tube as shown in Figure 1.6.
2. Add half a spatula of zinc powder, Zn into the solution.
3. Gently heat the mixture.
4. Filter the mixture into a test tube.
5. Add sodium hydroxide, NaOH solution into the filtrate to confirm the presence of iron(II) ion, Fe2+.
6. Record all observations.
Data and observation:
Construct a suitable table to record all observations in section A and section B.
Discussion:
1. For each conversion in sections A and B, identify the substances that are oxidised or reduced.
Give reasons for your answers in terms of:
(a) change in the oxidation number.
(b) transfer of electron.
2. What is the role of bromine water, Br2 in section A and zinc powder, Zn in section B?
Give your reasons.
3. Why is freshly prepared iron(II) sulphate, FeSO4 solution used for the experiment in section A?
4. Name a reagent that can be used to verify the presence of iron(III) ion, Fe3+ in section A and iron(II) ion, Fe2+ in section B.
5. Suggest another substance that can replace bromine water, Br2 in section A and zinc powder, Zn in section B.
Answer:
Result:
Table to record all observations in Sections A and B.
1.
Section A:
(a) Fe2+ ions are oxidised because the oxidation number of iron in iron(II) sulphate increases from +2 to +3, while bromine water is reduced because the oxidation number of bromine decreases from 0 to -1.
(b) Fe2+ ions are oxidised because Fe2+ ions lose electrons to form Fe3+ ions and bromine water is reduced because bromine molecule, Br2 gains electrons to form bromide ion, Br−.
Section B:
(a) Zinc is oxidised because the oxidation number of zinc increases from 0 to +2, while Fe3+ ion is reduced because the oxidation number of iron decreases from +3 to +2.
(b) Zinc is oxidised because zink atom, Zn loses electrons to form Zn2+ ion, and Fe3+ ion is reduced because Fe3+ gains an electron to form Fe2+ ion.
2. – Bromine water is an oxidising agent because bromine is the electron acceptor.
– Zinc is a reducing agent because zinc is the electron donor.
3. Iron(II) sulphate solution is easily oxidised to become iron(III) sulphate.
4. Sodium hydroxide solution.
5. Section A : Chlorine water
Section B : Magnesium powder
Aim: To study the conversion of iron(II) ion, Fe2+ to iron(III) ion, Fe3+ and vice versa.
Materials: 0.5 mol dm−3 of iron(II) sulphate, FeSO4 solution (freshly prepared), 0.5 mol dm−3 of iron(III) chloride, FeCl3 solution, bromine water, Br2 , zinc powder, Zn and 2.0 mol dm−3 of sodium hydroxide, NaOH solution.
Apparatus: Boiling tube, test tube, boiling tube holder, dropper, spatula, filter funnel, filter paper, Bunsen burner and test tube rack.
Procedure:
A. Conversion of iron(II) ion, Fe2+ to iron(III) ion, Fe3+
1. Pour 2 cm3 of 0.5 mol dm−3 of iron(II) sulphate, FeSO4 solution (freshly prepared) into a boiling tube held by a boiling tube holder as shown in Figure 1.5.
2. Using the dropper, add bromine water, Br2 while shaking the boiling tube until no further colour change can be observed.
3. Gently heat the mixture in the boiling tube.
4. Add sodium hydroxide, NaOH solution into the mixture to confirm the presence of iron(III) ion, Fe3+.
5. Record all observations.
B. Conversion of iron(III) ion, Fe3+ to iron(II) ion, Fe2+
1. Pour 2 cm3 of 0.5 mol dm−3 of iron(III) chloride, FeCl3 solution into a boiling tube as shown in Figure 1.6.
2. Add half a spatula of zinc powder, Zn into the solution.
3. Gently heat the mixture.
4. Filter the mixture into a test tube.
5. Add sodium hydroxide, NaOH solution into the filtrate to confirm the presence of iron(II) ion, Fe2+.
6. Record all observations.
Data and observation:
Construct a suitable table to record all observations in section A and section B.
Discussion:
1. For each conversion in sections A and B, identify the substances that are oxidised or reduced.
Give reasons for your answers in terms of:
(a) change in the oxidation number.
(b) transfer of electron.
2. What is the role of bromine water, Br2 in section A and zinc powder, Zn in section B?
Give your reasons.
3. Why is freshly prepared iron(II) sulphate, FeSO4 solution used for the experiment in section A?
4. Name a reagent that can be used to verify the presence of iron(III) ion, Fe3+ in section A and iron(II) ion, Fe2+ in section B.
5. Suggest another substance that can replace bromine water, Br2 in section A and zinc powder, Zn in section B.
Answer:
Result:
Table to record all observations in Sections A and B.
1.
Section A:
(a) Fe2+ ions are oxidised because the oxidation number of iron in iron(II) sulphate increases from +2 to +3, while bromine water is reduced because the oxidation number of bromine decreases from 0 to -1.
(b) Fe2+ ions are oxidised because Fe2+ ions lose electrons to form Fe3+ ions and bromine water is reduced because bromine molecule, Br2 gains electrons to form bromide ion, Br−.
Section B:
(a) Zinc is oxidised because the oxidation number of zinc increases from 0 to +2, while Fe3+ ion is reduced because the oxidation number of iron decreases from +3 to +2.
(b) Zinc is oxidised because zink atom, Zn loses electrons to form Zn2+ ion, and Fe3+ ion is reduced because Fe3+ gains an electron to form Fe2+ ion.
2. – Bromine water is an oxidising agent because bromine is the electron acceptor.
– Zinc is a reducing agent because zinc is the electron donor.
3. Iron(II) sulphate solution is easily oxidised to become iron(III) sulphate.
4. Sodium hydroxide solution.
5. Section A : Chlorine water
Section B : Magnesium powder