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

During electrolysis of aluminium, which of the following substance is used as an electrolyte?

  1. $Al _2O _3$
  2. $Al _2O _3, Na _3AlF _6$
  3. $Al _2O _3, Na _3AlF _6, CaF _2$

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

The substance which is used as an electrolyte during electrolysis of aluminium is $Al _2O _3, Na _3AlF _6, CaF _2$.

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

Anodic product in the electrolytic reduction of alumina:

  1. $CO _2, O _2$
  2. $O _2$
  3. $F _2$
  4. $O _2,F _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ionization of Alumina in Electrolytic refining.

$2Al _2O _3\longrightarrow 6O^{-2}+Al^{3+}$
Reaction at cathode
$4Al^{3+}+12e^{-}\longrightarrow 4Al$
Reaction at anode
$6O^{-2}\longrightarrow 3O _2+12e^-$
$O _2$ is released at anode.

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

Which of the following statements is correct?
(i) Copper is extracted by hydrometallurgy from low-grade ores.
(ii) In the electrolytic reduction of alumina, graphite is acting as an anode and steel vessel with the lining of carbon acts as an anode.
(iii) In Hall-Heroult process, aluminium is obtained at anode and CO and $CO _2$ are produced at the cathode.

  1. (i) only

  2. (i) and (ii) only

  3. (ii) and (iii) only

  4. All of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$(i)$ Copper is extracted by hydrometallurgy from low-grade ores. It is leached out using acid or bacteria. The solution containing $Cu^{2+}$ is treated with scrap iron or $H _2$.
$Cu^{2+} (aq)+H _2 (g)\longrightarrow Cu (s)+2H^+ (aq)$
$(ii)$ In the electrolytic reduction of alumina. The graphite act as anode and steel with a lining of carbon acts as an anode.
$(iii)$ The process of extracting Aluminium from Alumina $(Al _2O _3)$ by electrolysis is called Hall-Heroult process. In this process Aluminium is produced at cathode which is obtained by outlet, oxygen is released at an anode. It reacts with carbon of anode producing $CO$ and $CO _2$.
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Cryolite and fluorspar are mixed with $Al _2O _3$ during electrolysis for extraction of aluminium to:

  1. increase the mass of the reaction mixture

  2. get other products at anode like fluorine

  3. lower the melting point and increase the conductivity of the electrolyte

  4. reduce aluminium oxide by cryolite
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the metallurgy of Aluminium, purified $Al _2O _3$ is mixed with $Na _3AlF _6$ or $CaF _2$ which lowers the melting point of mix and brings conductivity.

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

In the metallurgy of aluminium:

  1. $Al^{3+} $ is oxdised to $Al _{(s)}$

  2. graphite anode is oxidised to carbon monoxide and carbon dioxide

  3. oxidation state of oxygen changes in the reaction at anode

  4. oxidation state of oxygen changes in the overall reaction involved in the process
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The oxidation state of $'O'$ does not change i neither the reaction occurring at the anode or the overall reaction as shown below.
At anode:-$C+{ O }^{ 2- }\longrightarrow CO+2{ e }^{ - };C+2{ O }^{ 2- }\longrightarrow C{ O } _{ 2 }+4{ e }^{ - }$
The released electrons used at cathode and here Graphite  is oxidized to $'CO'$ and $C{ O } _{ 2 }$
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

In the extraction of aluminium,
Process X: applied for red bauxite to remove iron oxide (chief impurity)
Process Y: applied for white bauxite to remove Z (chief impurity). 

Then, Process X and impurity Z are:

  1. X $=$ Hall - Heroults process & Y$=$ $SiO _{2}$
  2. X $=$ Bayers process and Z $=$ $SiO _{2}$
  3. X $=$ Serpecks process and Y $=$ iron oxide
  4. X $=$ Baeyers process and Y $=$ iron oxide
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Bayer's process is used for beneficiation of red bauxite.
Serpeck's process is used for beneficiation of white bauxite. 
Reaction to remove impurity from white bauxite is:
$SiO _2+2C\rightarrow Si+2CO$ .