Aluminium is extracted commercially from its ore by
A. heating aluminium oxide with coke in a furnace
B. the electrolysis of fused aluminium oxide in cryolite
C. treating cryolite with sodium hydroxide solution under pressure.
D. heating sodium aluminium silicate to a high temperature.
Strong electropositive metals are usually extracted by electrolysis of their fused salts and not by reduction. Metals like sodium, potassium, calcium, magnesium, beryllium, and lithium, are not extracted by blast reduction, but by electrolysis. Weaker metals like copper, iron, lead, tin, gold, mercury, and silver, which are found in the lower parts of the electrochemical series can be extracted from their ores by heat reduction.
Now for the right answer to the above question:
- Option A is incorrect. aluminum oxide cannot be readily reduced to aluminum by blast reduction.
- Option B is correct. Yes, fused aluminum oxide is obtained when pure aluminum oxide is heated with cryolite to a molten form, this is to make aluminum the only positive ion at the cathode ready to be deposited during electrolysis.
- C is incorrect. wrong option.
- D is not the correct answer. Heating sodium aluminum silicate to a high temperature is also an attempt to used heat to reduce and obtain pure aluminum, this will also fail.
You may please note these/this:
- Highly electropositive metals tend to resist extraction by heat and blast reduction. They are usually effectively extracted by electrolysis of their fused pure salt.
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/ culled from 2016 JAMB-UTME Chemistry past question 17 /