C6.1 (3) - extractions

Question 1

define an ore

Answer 1

a mineral or rock that contains a high enough amount of a metal/metal compound so that the value of the metal is more than the cost of extracting it

Question 2

what is the ore to extract copper?

Answer 2

malechite

Question 3

what is the ore to extract iron?

Answer 3

haematite

Question 4

what is the ore to extract aluminum?

Answer 4

bauxite

Question 5

describe the 3 main stages to extract a metal from an ore

Answer 5

1) ore is mined

2) ore is processed
(metal compound removed from rock)

3) metal is extracted from metal compound

Question 6

what is the mneunomic to remember the metal reactivity series?
(and what does each stand for - in terms of elements)

Answer 6

pink - potassium
smiling - sodium
cats - calcium
meow - magnesium
at - aluminium
cute - carbon (NOT METAL)
zebras - zinc
in - iron
the - tin
long - lead
hot - hydrogen (NOT METAL, USED FOR REFERENCE) 
curly - copper
swirly - silver
grass - gold
privately - platinium

Question 7

why is carbon used to extract metals instead of electrolysis?

Answer 7

as electrolysis is expensive

- so instead, carbon is used to reduce the wanted metal from its oxide

Question 8

all metals can be extracted from their compounds using …… but is expensive

Answer 8

electrolysis

Question 9

why can copper be extracted using carbon, but not sodium?

Answer 9

as copper is less reactive than carbon

- wheras sodium is too reactive to be extracted by reduction

Question 10

describe the 2 main steps of how copper is extracted from copper sulfide
(and the word and symbol equation for each one)

Answer 10

1) copper sulfide (II) is heated in air
(to get it into metal oxide form for carbon to reduce later)

copper (II) sulfide + oxygen -> copper (II) oxide + sulfur dioxide
2CuS(s) + 3O (g) -> 2CuO(s) + 2SO (g)
2 2

2) copper oxide is heated with carbon

copper (II) oxide + carbon -> copper + carbon dioxide
2CuO(s) + C(s) -> 2Cu(s) + CO (g)
2

Question 11

explain how the extraction of copper sulfide is a redox reaction
- and what is the reducing agent

Answer 11

• copper(II) oxide loses oxygen and is reduced
• carbon gains oxygen and is oxidised
• carbon is the reducing agent (reduced copper oxide to copper)

Question 12

what form of carbon is used when extracting copper from copper sulfide?

Answer 12

charcoal

Question 13

what is the machinery used to extract iron from its ore called?

Answer 13

a blast furnace

Question 14

what are the raw materials used to extract iron?

and what is each one’s function

Answer 14

• iron ore (haematite - contains iron needed for extraction)
• coke (reduces iron(III) oxide to iron)
• limestone (purifies iron)

Question 15

describe the three steps in which iron is extracted

- and the symbol equation for each one

Answer 15

1) coke burns in hot air, making carbon dioxide
C(s) + O (g) -> CO (g)
2 2

2) more coke reduces carbon dioxide to carbon monoxide
C(s) + CO (g) -> 2CO(g)
2

3) carbon monoxide reduces iron(III) oxide to iron
3CO (g) + Fe O -> 3CO (g) + 2Fe (l)
2 2 3 2

Question 16

what is the main reducing agent in the blast furnace for extracting iron from iron(III) oxide?
(and why can it do so)

Answer 16

carbon monoxide

- it is more reactive than iron

Question 17

in what state does iron leave the blast furnace?

Answer 17

molten state (temperatures are very high, 1500C)

Question 18

how is extracted iron purified?

Answer 18

• using limestone

1) calcium carbonate decomposes to calcium oxide and carbon dioxide
2) calcium oxide reacts with silica from impurities from extracted iron

Question 19

how does purified iron leave the blast furnace?

Answer 19

• as molten calcium silicate/slag floats on the molten iron (as it is less dense)
• iron leaves from bottom tube in liquid state
• slag leaves from tube on top of it

Question 20

what does impure iron contain?

Answer 20

sandy impurities

Question 21

why is the reaction between calcium oxide and silica a neutralization reaction?

Answer 21

as calcium oxide is slightly alkalinic

and silica is slightly acidic

Question 22

how does a blast furnace work?

Answer 22

• hot air forced in at the bottom of furnace = high temperature
• raw materials added to top of blast furnace (iron ore oxide, coke, limestone)
• they react together at a high temperature

Question 23

what is coke?

Answer 23

• a compound made of mostly carbon

- formed by heating coal in the absence of air

Question 24

why is electrolysis used to extract some metals from their ores?
(and give an example)

Answer 24

if they are more reactive than carbon

ie. aluminum

Question 25

why is aluminium oxide dissolved in molten cryolite?

Answer 25

• as electrolysis only works if the compound is in solution or molten (so ions can move)
• melting point of aluminium oxide is very high
• and aluminum oxide does not dissolve in water
• cryolite lowers melting point of aluminium oxide from 2000C to 950C

Question 26

what is the structure which allows aluminium to be extracted from aluminium oxide? (the structure=container where extraction occurs)

(and what is it made of)

(4)

Answer 26

huge electrolysis cell

• carbon anodes
• carbon lining of cell (cathode)
• insulation on outside of cell
• small hole at bottom of cell for purified molten aluminium to flow through

Question 27

what is produced at the cathode and anode during electrolysis/extraction of aluminium?

(is it oxidation/reduction)

Answer 27

cathode (-) = aluminium ions are reduced (gain electrons)

anode (+) = oxygen ions are oxidised (lose electrons)

Question 28

2 reasons why extraction of aluminium is expensive

Answer 28

• requires electricity (for electrolysis)

- carbon anodes constantly need replacing as oxygen reacts with carbon to produce carbon dioxide

Question 29

how is aluminium oxide seperated?

Answer 29

• as in molten state, Al3+ ions and O2- ions are free to move around
• so aluminium is reduced by the carbon lining of cell and becomes molten aluminium
• as it is more dense than the aluminium oxide cryolite solution, it sinks
• and leaves the cell through the tapping hole (molten)
• oxygen ions are oxidised by the suspended carbon anodes
• and later react with the carbon and produce carbon dioxide

Question 30

environmental downside of extracting aluminium?

Answer 30

released carbon dioxide which is a greenhouse gas

Question 31

write the half equations that happen at each electrode when aluminium oxide is extracted

Answer 31

cathode:
Al3+ + 3e- -> Al

anode:
2O2- -> O + 4e-
2

Question 32

what material lines the cathode and anode in the extraction of aluminium?

Answer 32

graphite

Question 33

name 2 examples of alternative biological methods of metal extraction (and describe each one briefly)

Answer 33

bioleaching

• when bacteria breaks down low grade ores to metal compounds
• and produce leachate solutions with dissolved metal compounds
• this process occurs naturally, but bacteria speed up this reaction

phytoextraction

• when plants absorb metal compounds from low-grade soil
• trapped within leaves/stem
• then burned to extract metlas

Question 34

how are the metals in bioleaching extracted?

Answer 34

Bioleaching is a technique that makes use of bacteria to extract metals from metal ores
Some strains of bacteria are capable of breaking down ores to form acidic solutions containing metals ions such as copper(II)
The solution is called a leachate which contains significant quantities of metal ions
The ions can then be reduced to the solid metal form and extracted by displacement reactions or electrolysis
This method is often used to extract metals from sulfides e.g. CuS or Fe2S
Although bioleaching does not require high temperatures, it does produce toxic substances which need to be treated so they don’t contaminate the environment
Bioleaching is not only used for the primary extraction of metals, but it is also used in mining waste clean up operations

Question 35

why do bacteria cause the process of bioleaching to occur?

Answer 35

• similar to how we get energy from respiration

- bacteria get energy from breaking bonds

Question 36

positives of bioleaching?

Answer 36

• energy efficient (compared to electrolysis)
• cheaper than traditional mining and processing
• no toxic greenhouse gases released

Question 37

negatives of bioleaching?

Answer 37

• very slow
• toxic substances usually produced (must take care )

Question 38

what allows metals to be extracted through phytoextraction?

Answer 38

• plant is burned
• ash contains a high concentration of metals
• which are extracted

Question 39

what does a complexing agent do?

Answer 39

allows plants to absorb ions more easily (during phytoextraction)

Question 40

positives of phytoextraction? (3-4:

Answer 40

• cheaper than mining or processing
• less energy needed
• close to carbon neutral (carbon dioxide released when burning is absorbed when growing)
• allows a high concentration of metals to be extracted from low grade ores

Question 41

negatives of phytoextraction? (2-3)

Answer 41

• very slow
• (only certain plants absorb certain metal compound)
• may take many years of replanting and harvesting before plants start taking up the metal compounds

Question 42

what is good about phytoextraction and bioleaching?

Answer 42

both can extract metals from low-grade ores (which would have been unviable)

• and some ores are becoming scarce

Question 43

which substance do you use to absorb all water? (compound)

Answer 43

• anhydrous calcium chloride