Question

(a) Name the metal which is extracted from haematite ore?
(b) Name one ore of aluminium. Name the aluminium compound present in this ore and write its chemical formula.
(c) How is aluminium metal extracted? Explain with the help of an equation.
(d) Name the electrode at which aluminium metal is produced.
(e) Which gas is produced during the extraction of aluminium? At which electrode is this gas produced?
​(f) What is an alloy? Name two alloys of aluminium.

Answer 1

(a) The metal extracted from hematite ore is iron.

(b) Bauxite is an ore of aluminium. The aluminium compound present in this ore is aluminium oxide. Its chemical formula is ${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}$.

(c) Aluminium is extracted by electrolytic reduction of its molten oxide. Aluminium is a highly reactive metal and it is placed at the top of the reactivity series. It cannot be reduced by other reducing agents such as coke, carbon monoxide, etc..
On passing electricity through molten aluminium oxide, decomposition reaction occurs and formation of aluminium metal and oxygen gas takes place.

${\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{l}\right)\stackrel{\mathrm{electrolysis}}{\to }4\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)$

Molten aluminium oxide consists of aluminium and oxide ions. The reaction that occurs during electrolysis are:
1) Cathode produces electrons to reduce aluminium ions to aluminium atoms by acting as a reducing agent. Aluminium ions are cations, therefore, they get attracted to negatively charged cathode and get deposited there

${\mathrm{Al}}^{+3}+3{\mathrm{e}}^{-}\to \mathrm{Al}$

2) Oxide ions are anions, therefore, they get attracted to the positively charged anode. These oxide ions are oxidized to oxygen gas. Oxygen gas is produced at the anode.

$2{\mathrm{O}}^{-2}\to {\mathrm{O}}_2+4{\mathrm{e}}^{-}$

(d) Aluminium metal is produced at the cathode. During electrolysis, cathode produces electrons to reduce aluminium ions into aluminium atoms by acting as a reducing agent. Aluminium ions are cations, therefore, they get attracted to negatively charged cathode and get deposited there.

${\mathrm{Al}}^{+3}+3{\mathrm{e}}^{-}\to \mathrm{Al}$

(e) Oxygen gas is produced during the extraction of aluminium. The oxygen gas is produced at the anode. During electrolysis, aluminium atoms are deposited at cathode, whereas oxide ions, being anions, get attracted to the positively charged anode. These oxide ions are oxidized to oxygen gas. Oxygen gas is produced at the anode.

$2{\mathrm{O}}^{-2}\to {\mathrm{O}}_2+4{\mathrm{e}}^{-}$

(f) When a metal is mixed with another element (metal or a non-metal) such that a new substance of homogeneous composition is obtained, the substance obtained is known as an alloy. For eg. Al-Li alloy (lithium), Alnico (aluminium, nickel, copper).