Iron and its compound

Electron configuration of Iron

[Ar]3d⁶4s²

Properties of iron as a transition element

1. Forms coloured compounds; for instance Fe²⁺ is green
2. Has variable oxidation states; +2, +3,
3. Forms complexes, e.g. Fe(CN)₆^3-.
4. Has catalytic properties, e.g., iron catalyze formation of ammonia from nitrogen and hydrogen.

Extraction of iron

Iron, which is the second most abundant metal occurring in the earth’s crust, is extracted from its ores which are;

haematite,           Fe₂O₃

magnetite,           Fe₃O₄,

siderite,                FeCO₃.

Extraction of iron from hematite

Main Impurities

Silica, SiO₂

Procedure

Iron ore, limestone and coke in the correct proportions are reacted with

Preheated air in a blast  furnace.

Reactions leading to reduction of iron oxide are

 C (s) + O₂ (g)  →CO₂ (g)

 CO₂ (s) + C (s)  →2CO (g)

Fe₂O₃ (s) + 3CO (g) → 2Fe (s) + 3CO₂ (g)

Reactions leading to removal of impurities

 CaCO₃ (s) → CaO (s) + CO₂ (g)

CaO (s) + SiO₂ (s)  → CaSiO₃ (l)

CaO (s) + Al₂O₃ (s)  → CaSiO₃ (l)  slag

Molten iron and slag percolate to the bottom of the furnace and taped of through different taps.

Trial  1

In the production of iron metal, haematite, Fe₂O₃, is mixed with coke and limestone and heated in a blast furnace.

(a) What is the purpose of adding

(i) limestone (1 mark)

(i) coke?     (1 mark)

(b) Write three different equations for the reaction in which haematite are converted into iron in the blast furnace. (3marks)

(c) Explain why it is possible to extract iron by the method described above.         ( 2 marks)

(d) (i) Name one other method that can be used to extract iron from its ore.       ( 1 marks)

(ii) Suggest a reason why the method you have named in d(i) is not used commonly in the production of iron.

Oxidation states of Iron

Iron has oxidation states +2 and +3

Oxidation state Fe³⁺ ([Ar]3d⁵) is more stable than F²⁺ ([Ar]4s¹3d⁵) because Fe³⁺ has stable half-full electron configuration.

Trial 2

This explains why green iron II compounds rapidly turn into brown iron III compounds.

Properties of iron

Pure iron is a silvery colored metal with a melting point of 1535⁰C and boiling point 3000⁰C.

 It is a soft, ductile and malleable metal, which is strongly ferromagnetic.

Rusting of iron

Iron in presence water and air form a brown coat called rust or hydrated iron (III) oxide, Fe₂O₃.xH₂O,

Disadvantage of rusting

• Weaken tools
• Makes objects look ugly

Methods of preventing rusting

(a) Keeping objects in dry places.

(b) Painting

(c) Oiling

(d) Greasing

(e) Coating with another metal.

(f) Zinc plating

The reaction of iron with water

Iron does not react with cold water but with steam to form blue-black tri-iron trioxide oxide

3Fe(s) + 4H₂O(g)   → Fe₃O₄(s) + 4H₂(g)

Reaction of iron with acids

Iron displaces hydrogen readily from dilute hydrochloric acid and sulphuric acids, forming iron (II) salts. Dilute nitric acid forms iron (II) nitrate and oxides of nitrogen.

Fe(s) + 2HCl(aq) → FeCl₂ (aq) 2H₂(g)

Fe(s) + H₂SO₄(aq) →FeSO₄(aq) + H₂(g)

Concentrated H₂SO₄ gives a mixture of ferrous and ferric sulphates.

Fe(s) + 2H₂SO₄(aq) →  FeSO₄(aq) + SO₂(g) + 2H₂O(l)

2FeSO₄ (aq) + 2H₂SO₄ (aq) →  Fe₂(SO₄)₃ (aq) + 2H₂O (l) + SO₂ (g) 

Action of alkalis, halogen and sulphur on iron

Iron does not react with alkalis.

Halogens and sulphur combine with the heated metal forming halides and sulphide respectively.

2Fe(s) + 3Cl₂(g) → 2FeCl₃ (g)

Fe(s) + S(s)  →   FeS (s)

Displacement of less electropositive metals

Iron displaces copper from a solution of copper sulphate.

Fe(s) + Cu²⁺(aq) →  Fe²⁺(aq) + Cu(s)

Hydrolysis of Iron III slats in water

Iron III salts hydrolyze in water to form an acidic solution

Fe³⁺(aq) + 3H₂O(l) →   Fe(OH)₃(s) +3H⁺(aq)

Consequently, Iron III solution

• turns blue litmus paper red.
• Liberate carbon dioxide from carbonates with the formation of brown precipitate
• Has pH less than 7

Reaction iron III solution with sodium carbonate solution

2F³⁺(aq) + 3CO₃^2-(aq) + 3H₂O(l)    → 2Fe(OH)₃(s) + 3CO₂(g)

Observation

A brown ppt. formed with effervescence

Trial 3

State what would be observed and write an equation for the reaction that takes place when aqueous iron (III) chloride with sodium carbonate                                         (3½ marks)

Reactions of iron (III) as an oxidizing agent

Iron (III) compounds are strong oxidizing agents, for instance, it oxidizes iodide ions (I^–) to iodine and tin (II) compounds to tin (IV) compounds and itself reduced to Fe²⁺ compounds.

2Fe³⁺(aq) + 2I^–(aq) → 2F²⁺(aq) + I₂(aq)

2Fe³⁺(aq) + Sn²⁺(aq)  → 2F²⁺(aq) + Sn²⁺(aq)

Trial 4

A solution of Iron (III) chloride was added to an aqueous solution of tin (II) chloride acidified with hydrochloric acid and the mixture shaken.

(a) State what was observed. (1 mark)

(b) Write an equation for the reaction that took place.

Qualitative analysis of Fe²⁺ salt

Common iron II salts include

•  Ferrous sulphate: FeSO₄.7H₂O
•  Ammonium ferrous sulphate (NH₄)₂Fe(SO₄)₂.6H₂O
•  Ferrous oxalate. FeC₂O₄

• Addition of dilute sodium hydroxide or ammonia solution

Observation

A dirty green precipitate insoluble in excess turn brown on standing.

Fe²⁺(aq) + 2OH^–(aq) → Fe(OH)₂(s)

• Confirming presence of Iron III ions

 Forms a deep blue solution with potassium hexacyanoferrate II.

 Forms a red solution with ammonium thiocyanate solution.

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Compiled by Dr. Bbosa Science