4 Changes Of Iron(ii) Ions To Iron(iii) And Vice Versa 5uv4e

Redox reaction that involve Fe2+ ion and ion Fe3+ ion Iron metal, Fe exhibits two oxidation states, that are Fe2+ and Fe3+. Did you know colour for Fe2+ ion and Fe3+ ion? Oxidation (loss e-)

Fe2+

Fe3+ Reduction (gain e-)

Conversion of ion Fe2+ to ion Fe3+ is an oxidation process because it involve of loss of electron;

2+

Fe

→

3+

Fe

+ 1e

The oxidation number of Fe increase from +2 to +3. Thus, oxidizing agent is needed to oxidized Fe2+ ion to Fe3+ . Oxidizing agents that can be use is; 1. chlorine water, Cl2 2. liquid bromine, Br2 3. acidified potassium manganate(VII), KMnO4 4. acidified potassium dichromate(VI), K2Cr2O7 5. acidified hydrogen peroxide, H2O2 6. concentrated nitric acid, HNO3

start Fe2+ green

finish + chlorine water, liquid bromine + HNO3 concentrated + H2O2 + dilute sulphuric acid solution + KMnO4 acidic + K2Cr2O7 acidic

Fe3+ brown

observation : The solution colour turn from green to brown HOW this process is made / possible? i. 5 cm3 iron(II) sulphate solution of 0.1 mol dm-3, FeSO4 was pour into a test tube ii. bromine water is dropped into the solution iii. the test tube is shake and slowly heated until no changes occur HOW do you determine the present of iron(III) ion? (cation test) i. A few dropped of ammonia solution / ammonium hydroxide is added, until it excess into a test tube. ii. A brown precipitate, insoluble in excess NH4OH / NaOH is formed Half equation : Fe2+ → Fe3+ + 1e - ion iron(II) is under goes oxidation Half equation : Br2 + 2e → 2Br- bromine undergoes reduction process

Oxidizing agent : bromine water, Br2 Reduction agent: iron(II) , Fe2+ x2 half equation : 2Fe2+ → 2Fe3+ + 2e half equation: Br2 + 2e → 2Brtotal ionic equation : 2Fe2+ + Br2 → 2Fe3+ + 2Br-

Conversion of ion Fe3+ to ion Fe2+ is a reduction process because it involve accepting electron Fe3+ + 1e →

Fe2+

So reduction agent is needed to reduced ion Fe3+to ion Fe2+. The reduction agent that involve is: 1. 2.

magnesium metal, aluminium, zinc sulphur dioxide gas, SO2

start

finish +

Fe3+

Dilute H2SO4 solution, Then flow SO2 gas into the solution

Fe2+ Brown

zinc pieces, then heat the mixture

observation: changes from brown to green

green

how this process is made? i. 5 cm3 iron(III) sulphate solution of 0.1 mol dm-3, Fe2(SO4)3 is pour into the test tube ii. one spatula of zinc powder is pour into the test tube iii. shake the test tube and slowly heated until has no changes occured How to determined the present of iron(II) ion? i. ammonia solution / ammonium hydroxide is added gradually until excess into the test tube. ii. A dirty green precipitate, insoluble in excess NH4OH /NaOH is obtain half equation : Fe3+ + 1e → Fe2+ - iron(III) ion is reduced - iron(III) ion act as oxidizing agent half equation: Zn → Zn2+ + 2e - zinc is oxidizes - zinc act as reducing agent Ionic equation : 2Fe3+ + Zn → 2Fe2+ + Zn2+ Confirmation test present of Fe2+ or Fe3+

Cation potassium hexacyanoferrate (II) Fe2+ Blue precipitate Fe3+

Dark blue precipitate

Potassium hexacyanoferrat e (III) Dark blue precipitate Greenly brown solution

Potassium thiocyanate No red colour blood red colour

Prepared by; Kamal Ariffin SMKDBL, 2008