✅ C617-618, extracting iron + aluminium

Question 1

How is iron extracted from its ore - what machinery

Answer 1

Using a large reaction container called a blast furnace

Question 2

3 raw materials added to the top of the blast furnace - why

Answer 2

• iron ore, such as haematite, which contains iron(III) oxide
• coke
• limestone, which is used to purify the iron

Question 3

What is coke - hows it made

Answer 3

Coke, is mostly carbon,

- is made by heating coal in the absence of air

Question 4

What’s forced in at the bottom of the blast furnace

Answer 4

Hot air

Question 5

REACTIONS IN A BLAST FURNACE - (1)

- what is formed - to be the main reducing agent in the blast furnace, and how it formed, brief

Answer 5

• Carbon can reduce iron(III) oxide to iron, but carbon monoxide is the main reducing agent in the blast furnace
• carbon monoxide is formed when coke reacts with carbon dioxide

Question 6

3 stages to which iron(III) oxide is reduced in blast furnace

• involving prior to reduction what happens
• with symbol equations + state symbols

Answer 6

1 - Coke burns in the hot air, making carbon dioxide

C(s) + O2 —> CO2(g)

2 - More coke reduces the carbon dioxide, making carbon monoxide:

C(s) + CO2(g) —> 2CO(g)

3 - Carbon monoxide reduced iron(III) oxide to iron at around 1500C:

3CO(g) + Fe2O3(s) —> 3CO2(g) + 2Fe(l)

Question 7

Once carbon monoxide has reduced iron(III) oxide to iron, what next? - in English words

Answer 7

• the molten iron trickles downwards in the blast furnace
• it contains sandy impurities from the iron ore
• these are removed using the limestone, which is mostly calcium carbonate

Question 8

HOW are sandy impurities removed from the molten iron then

• 2 stages
• with symbol equations + state symbols

Answer 8

1 - Calcium carbonate (limestone) decomposes in the high temperatures:

CaCO3(s) —> CaO(s) + CO2(g)

2 - The calcium oxide formed reacts with silica from the sandy impurities to form calcium silicate.

CaO(s) + SiO2(g) —> CaSiO3(l)

Question 9

WHAT is formed when the calcium oxide reacts with silica from the sandy impurities - and what happens then

Answer 9

Molten calcium silicate - called slag

It floats on the molten iron, and both the iron and slag are removed separately at the bottom of the blast furnace

SEE FIG 2 PAGE 208

Question 10

4 uses of aluminium - not necessarily needed to know

Answer 10

Aircraft, overhead electricity cables, cooking foil, drinks cans

Question 11

Aluminium

- how it exists

Answer 11

Aluminium exists naturally, mainly as Aluminium oxide, Al2O3, found in an ore called bauxite

Question 12

Aluminium
- reactivity vs carbon
+ so… w/ problem

Answer 12

Aluminium is more reactive than carbon
- this means that, unlike iron and copper, it must be extracted from its ore by electrolysis

Problem:
- electrolysis only works if the compound is in solution or if it is molten — but aluminium oxide does not dissolve in water and its melting point is very high

Question 13

Melting point of aluminium oxide

Answer 13

• Al2O3 - mp = over 2000C - so very difficult to heat aluminium oxide to this temperature

Question 14

SOLUTION to how aluminium oxide is electrolysed

Answer 14

• melting point too high - prev card
• to get around this problem, aluminium oxide is dissolved in molten cryolite
• cryolite has a much lower melting point than aluminium oxide, and allows electrolysis to happen at about 950C

Question 15

Aluminium oxide solubility in water?

Answer 15

Aluminium oxide is insoluble in water

Question 16

Electrolysis process of aluminium

Cathode?

Answer 16

• the molten mixture of aluminium oxide and cryolite is contained in a huge electrolysis cell - made from steel, lined with graphite
• the graphite lining acts as the cathode, the negative electrode

Question 17

Electrolysis process of aluminium

Anode?

Answer 17

• a series of large graphite blocks act as the anodes , the positive electrodes

Question 18

What happens at cathode + anode during electrolysis of aluminium oxide

(3)

Answer 18

• aluminium is produced at the cathode
• oxygen is produced at the anode

The oxygen reacts with the hot graphite anodes, making carbon dioxide

Question 19

Electrode reactions that happen during electrolysis of aluminium - half equations

Answer 19

At cathode:

Al3+ + 3e- —> Al

At anode:

2O2- —> O2 + 4e-

Question 20

Even though aluminium is more abundant than iron in the Earth’s crust, aluminium is more expensive than iron.

Why?

Answer 20

This is mainly because of the large amounts of electrical energy used in the extraction process.

Question 21

Why must aluminium be extracted using electrolysis?

Answer 21

Aluminium is more reactive than carbon so it must be extracted from its compounds using electrolysis.

Question 22

ALUMINIUM ELECTROSLSI

The oxygen reacts with the carbon __, forming __ dioxide. So the __ gradually burn away. They must be __ frequently, adding to the __ of producing aluminium.

Answer 22

The oxygen reacts with the carbon anodes, forming carbon dioxide. So the anodes gradually burn away. They must be replaced frequently, adding to the cost of producing aluminium.

Question 23

Overall reactions in a blast furnace - pb

Answer 23