14.4 Extracting metals

Question 1

Methods of extraction

Answer 1

1. Reduction with carbon

2. Electrolysis

Question 2

Reduction with carbon

Answer 2

• heating metal compound with carbon (lesser reactive metals)
• zinc to silver

Question 3

Electrolysis

Answer 3

• using electricity to decompose the molten and metal compound (more reactive, compounds harder to break down)
• potassium to magnesium

Question 4

Extracting iron

Answer 4

• iron is extracted from haematite (iron ore) in a blast furnace
• most impt ore of iron
• composed mainly of iron (II) oxide (Fe2O3) and sand impurities (SiO2)

Question 5

Blast furnace

Answer 5

• tall, chimney-like
• made of bricks
• lined with refractory material (aluminium oxide, magnesium oxide which have high mp to trap heat)

Question 6

Chemical reaction

Answer 6

1. Production of carbon dioxide
2. Production of carbon monoxide
3. Reduction of haematite to iron
   4, Removal of impurities

Question 7

Production of carbon dioxide

Answer 7

• coke (carbon) burns in hot air
• Heat is produced
• carbon dioxide is produced
• C(s) + O2 (g) —> CO2 (g)
• exothermic reaction
• temperature of furnace increases to over 1600 degrees

Question 8

Production of carbon monoxide (CO)

Answer 8

• carbon dioxide further reacts with hot coke
• carbon dioxide is reduced by more coke present in the furnace to form carbon monoxide
• CO2 (g) + C(s) —> 2CO(g)

Question 9

Reduction of iron (II) oxide

Answer 9

• carbon monoxide (reducing agent) reduces iron (III) oxide
• molten iron and carbon dioxide are produced
• *Fe2O3 (s) + 3CO (g) —> 2Fe (L) + 3CO2
• 2Fe (L) sinks to bottom of furnace (cast iron)
• 3CO2 escapes as hot waste gases thru the top of the furnace, together with N2 and CO

Question 10

Removal of impurities

Answer 10

• limestone consists of calcium carbonate which decomposes at high temps
• carbon dioxide and carbon oxide are produced
• CaCO3 (s) —> CaO (s) + CO2 (g)
• calcium oxide reacts with silicon (IV) oxide (sand) in the iron ore
• calcium silicate (slag) is formed
• acid based reaction
• CaO (s) + SiO2 (s) —> CaSiO3 (L)
• CaSiO3 : also known as slag/calcium silicate
• sinks but is less dense than iron, so floats on top of molten iron