Others

Question

For the extraction of aluminium, write

(i) The most important ore.

(ii) One method for the purification of the mentioned ore.

(iii) The role of cryolite and calcium fluoride in electrolysis.

Solution

i) Bauxite (A1₂O₃ . 2H₂O) is the most important ore of aluminium.

(ii) Hall’s Process of purification of Bauxite : Bauxite ore is first fused with sodium carbonate. The Al₂O₃ forms sodium meta aluminate with sodium carbonate. The fused mass is now extracted with water where Fe₂O₃ and SiO₂remain insoluble in the residue.

Al₂O₃ +Na₂CO₃ --> 2NaAlO₃ +CO₂
This solution is warmed to 50 - 60°C and then CO₂ is passed through it. Al(OH)₃ is separated out as precipitate.

2NaAlO₂ +CO₂ +3H₂O --> 2Al(OH)₃ +Na₂CO₃
Now the precipitate of Al(OH)₃ is filtered, washed and dried up.

(iii) Role of cryolite and calcium fluoride : The pure alumina is a bad conductor of electricity and has a fusion temperature of about 2000°C which is more than the boiling point of aluminium (1800°C). So, to overcome these difficulties a mixture of alumina, cryolite and calcium fluoride in the ratio of 1 : 2 : 1 is used for electrolysis. This mixture is a good conductor of electricity and has a fusion temperature of 900°C.

Some More Questions From Others Chapter

What are the steps of the electro-thermic process for the manufacture of phosphorus from its mineral ?

Name the chief ore of lead. Write the steps involved in the extraction of lead from its sulphide ore by the self-reduction process. Give balanced equations wherever necessary.

Correct the following statements :

For water-system, the number of phases that can exist in equilibrium is two.

Complete the following statements by selecting the correct alternative from the choices given :

Mac Arthur-Forrest process is used for the extraction of:

Fill in the blanks choosing appropriate words given in brackets :

[Olefenic, aldol, safety matches, sodium sulphite, homolytic, organometallic, aldol condensation, flowers of sulphur, pesticides, heterolytic, antiknock, β-hydroxy-aldehyde, rat poison, sulphur dioxide, free radicals, antichlor, mixed condensation, photography, sodium hydroxide, charged species].

(i) Red phosphorus is used in the manufacture of__and.

(ii) Hypo is prepared by boilingsolution with_in alkaline medium.

(iii) The breaking of covalent bonds may be either through_or by__fission.

(iv) Acetaldehyde in presence of dilute alkali gives_and the reaction is called.

(v) TEL, an_compound, is used as an______agent.

Match the following :

(i) Write the equation which relates the number of phases, components and degree of freedom of a system in equilibrium.

(ii) How many phases and components are there in a system consisting of:

(1) a mixture of O₂ and N₂ gases

(2) N₂ gas containing H₂O vapour

(3) a mixture of ice and water

(4) a mixture of powdered iron and sulphur

(5) a lump of solid iron (II) sulphide

Give a suitable explanation, in brief, for your answer.