Tag: extraction of metals by electrolysis

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Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Cryolite is added to alumina as to lower the fusion temperature and make the mass good conductor of electricity.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Aluminium oxide has a very high melting point (over 2,000C), so it would be expensive to melt it. Instead, it is dissolved in molten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Identify the process to which the following reaction belongs : 


$\displaystyle { Al } _{ 2 }{ O } _{ 3 }.{ 2H } _{ 2 }O+{ Na } _{ 2 }{ CO } _{ 3 }\longrightarrow { 2NaAlO } _{ 2 }+{ 2H } _{ 2 }O+{ CO } _{ 2 }$

$\displaystyle { 2NaAlO } _{ 2 }+{ 2H } _{ 2 }O+{ CO } _{ 2 } \underrightarrow { 50-{ 60 }^{ o }C } { Al } _{ 2 }{ O } _{ 3 }.{ 2H } _{ 2 }O+{ Na } _{ 2 }{ CO } _{ 3 }$

  1. Hall's process

  2. Baeyer's process

  3. Serpeck's process

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Hall's Process: (Red bauxite)

Bauxite one + $Na _2CO _3 \xrightarrow{Fused} NaAlO _2$
                                                          $\downarrow $ extracted with water
                                                    Solution
                                                          $\downarrow$ warmed $50^o - 60^oC$
                                                   $CO _2$ is circulated
                                                          $\downarrow$
                                                   $Al(OH) _3 + Na _2CO _3$

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Which of the following statement(s) is/are correct"?

  1. The chemical processes in the production of steel from haematite ore involve reduction followed by

    oxidation.

  2. In Hall-Heroult process, the electrolyte used is a molten mixture of alumina and cryolite or fluorspar.

  3. Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,

  4. Haematitic, cassiterite, and argentite are oxide ores.
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

A) In the furnace, first the coke reacts with oxygen in the air blast to produce carbon monoxide(oxidation):$2C+O2\rightarrow 2CO$ The carbon monoxide reduces the iron ore (hematite) to molten iron, becoming carbon dioxide in the process:$3CO + Fe _2O _3\rightarrow 2Fe + 3CO _2$
B) The HallHroult process is the major industrial process for smelting of alumina. It involves dissolving alluminium oxide(allumina) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell.
C) Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,
D) Haematitic($Fe _2O _3$),cassiterite ($SnO _2$) and argentite($Ag _2S$).So Haematite and cassiterite are oxide ores but argentite is sulphide ore.Incorrect.
Hence options A,B & C are correct.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Aluminium is extracted from alumina $(Al _2O _3)$ by electrolysis of a molten mixture of:

  1. $Al _2O _3 + HF + NaAlF _4$
  2. $Al _2O _3+CaF _2+NaAlF _4$
  3. $Al _2O _3+Na _3AlF _6+CaF _2$
  4. $Al _2O _3+KF+Na _2AlF _6$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity. 

The fusion temperature of pure alumina is about 2000$^{\circ}$C and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminum is 1800$^{\circ}$C. 

These difficulties are overcome by using a mixture containing alumina$(Al _2O _3)$, cryolite $(Na _3AlF _6)$, and fluorspar $(CaF _2)$.

Therefore, the correct option is $C$
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

In the electrolytic reduction of alumina, the electrolyte is covered with coke powder because, if :

  1. prevents oxidation of aluminium formed

  2. reacts with aluminium forming aluminium carbide

  3. prevents heat loss from electrolyte

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electrolyte is a molten bath of cryolite and dissolved alumina. Cryolite is a good solvent for alumina with low melting point. The molten electrolyte is maintained at high temperature inside the insulating cell by using high amount of coke powder or dust to prevent the heat loss.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Aluminium is extracted by :

  1. Heating sodium aluminium silicate to a high temperature

  2. Treating cryolite with sodium hydroxide solution under pressure

  3. Heating aluminium oxide with coke in a furnace

  4. The electrolysis of molten aluminium oxide in fused cryolite
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aluminium is extracted by electrolysis. The ore is first converted into pure aluminium oxide by the Bayer Process and this is then electrolysed in solution in molten cryolite another aluminium compound. The aluminium oxide has too high a melting point to electrolyse on its own. The usual aluminium ore is bauxite.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

The electrolyte used in electrolytic refining of impure aluminium is:

  1. $AlF _3 + CaF _2$
  2. $Na _3AlF _6 + CAF _2$
  3. $AlF _3, Na _3AlF _6$ and $CaF _2$

  4. Any aluminium salt is molten state
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electrolytes are used to reduce melting point and increase conductivity.

$\therefore $ The electrolytes are $AlF _{6} , Na _{3}AlF _{6} , CaF _{2}$.