Question

ii) Write the cathode reaction in electrolytic reduction of alumina.
I) Name the process of concentration of bauxite.
iii) Write formula of Cryolite.
iv) Write the function of Cryolite.
v) Write an equation for the action of heat on aluminum hydroxide.​

Answer 1

ii ) When it is melted the Al3+ and O2- ions are free to move and conduct electricity. Electrolysis of the alumina/cryolite solution gives aluminium at the cathode and oxygen at the anode. 4Al3+ + 12e- → 4Al (aluminium metal at the (-)cathode) reduction.

i ) (a) The process for concentration of bauxite ore is Bayer's process (In which an ore of aluminium which is bauxite is heated in a pressure vessel along with a solution of sodium hydroxide also known as caustic soda at a temperature of 150 to 200oC . It is an ore of aluminium

iii ) Na3AlF6

iv ) It decreases the melting point of molten (liquid state) aluminium oxide from 2000 to 2500 °C to 900–1000 °C, and increases its conductivity thus making the extraction of aluminium more economical. Cryolite is used as an insecticide and a pesticide. It is also used to give fireworks a yellow color.

v ) The equation for the action of heat on aluminium hydroxide is as follows. 2 Al (OH) ₃ → Al₂O₃ + 3 H₂O. It essentially means that heat decomposes aluminium hydroxide into its components. It breaks down in the form of aluminium oxide and three molecules of water.

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