Bauxite Questions

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March 2013

No Bauxite questions
March 2012

No Bauxite questions
Nov 2012

2.9 During the extraction of aluminium from aluminium oxide, cryolite is added to ... (2)


2.9 D


March 2011

No Bauxite questions
Nov 2011

1.4 The name of the chemical substance in which Al2O3 is dissolved to lower its melting point during the industrial extraction of aluminium (1)
1.4 Cryolite


March 2010

3.5 Which ONE of the following statements about the extraction of aluminium is TRUE? (2)


3.5 C


Nov 2010

1.4 The type of electrochemical cell used in industry to produce elements such as chlorine and aluminium (1)
1.4 Electrolytic cell


March 2009

No Bauxite questions
Nov 2009 Unused

No Bauxite questions
Nov 2009

No Bauxite questions
Nov 2008

11 Aluminium is one of the most abundant metals on earth, yet it is expensive - largely because of the amount of electricity needed to extract it. Aluminium ore is called bauxite. The bauxite is purified to yield a white powder, aluminium oxide, from which aluminium can be extracted.

The diagram below shows an electrolytic cell used for the extraction of aluminium at temperatures as high as 10000C.



11.1 State the energy conversion that takes place in this electrolytic cell. (2)
11.1 Electrical energy to chemical energy

11.2 Is aluminium formed at the positive or negative electrode?
Write down POSITIVE or NEGATIVE only. (1)
11.2 negative

11.3 Use the Table of Standard Reduction Potentials (Table 4A or 4B) to write down
the half-reaction for the formation of aluminium. (2)
11.3

11.4 Explain why carbon dioxide gas is formed at one of the electrodes. (2)
11.4
Carbon will burn in (react with) O2 because of the high temperature to form CO2

OR



OR

The carbon is oxidised according to the following half-reaction:

11.5 Why should the carbon electrodes be replaced regularly? (2)
11.5 Carbon burns away (used up / oxidised / loses e-) and needs to be replenished)

11.6 Write down TWO negative effects that the extraction of aluminium can have on the environment. (2)
11.6 Any two:

Ecological Impact
• Loss of landscape due to the size of the chemical plant needed
• Disposal of red mud (iron(III) oxide formed during extraction of aluminium oxide from bauxite) into lagoons causing them to become unsightly

Environmental Impact
• Carbon dioxide from the burning of the anodes contributes to the (enhanced) greenhouse effect (air pollution /global warming)
• Carbon monoxide is poisonous
• fluorine (and fluorine compounds) lost from the cryolite during the electrolysis process is poisonous
• Alkali of red mud dams can drain into soil and contaminate groundwater
• Pollution caused by power generation (for electrolytic process) using coal-fired plants leads to acid rain/enhanced (greenhouse effect)
• Noise pollution


Prep Paper 2008

11.1 In an aluminuim smelter, aluminium metal is extracted from bauxite, a hydrated aluminium oxide, via an electrolytic process.

11.1.1 Write down the energy conversion that takes place in an electrolytic cell. (2)
11.1.1 Electrical energy to chemical energy

11.1.2 Write down the equation for the half-reaction responsible for the formation of aluminium in a smelter. (2)
11.1.2

11.1.3 Explain in terms of the relative strength of oxidising agents why the electrolytic production of aluminium requires more electrical energy than that of iron or copper. (2)
11.1.3 Aluminum has a lower reduction potential (-1,66V) and is hence a weaker oxidising agent compared to that of iron (-0,44V) and copper (+0,34V). The aluminium ions therefore require a large amount of energy to be reduced.

11.1.4 Name TWO advantages that the use of aluminium has over that of iron. (2)
11.1.4
It is much lighter for the same strength (or stronger for the same mass).
It is corrosion free.

11.2 A huge aluminium smelter is planned in Coega in the Eastern Cape. When operational, it will consume 1350 MW of electricity or 4% of the nation's total energy.

It is estimated that 5200 jobs will be created at the peak of construction. About 1000 workers will be employed on a full-time, permanent basis, and between 200 and 300 full-time subcontractors will also be direclty associated with the smelter.

11.2.1 Taking the present South African socio-economic realities into account, give ONE reason why the aluminium smelter should:

(a) Not be built (1)
(a)
It will consume a huge amount of electricity.
Will cause power failures

(b) Be built (1)
(b) It will create jobs
Create foreign investment
Contributes to GDP

11.2.2 Give ONE reason why environmental activists oppose the construction
of the smelter. (1)
11.2.2 The production of the large amount of electricity used enhances the greenhouse effect (or climate change)

OR

The process is responsible for the toxic waste of fluoride

OR

Pollution


Exemplar Paper 2008

No Bauxite questions
Additional Exemplar Paper 2008

1.4 The main ore from which aluminium is extracted (1)
1.4 Bauxite






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