General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 18

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Question 1
1 / -0

In the extraction of aluminium by electrolytic process, cryolite is added to ________.

A
lower the melting point of alumina

B
increase the electrical conductivity

C
minimise the anode effect

D
remove impurities from alumina

Solution

In the extraction of aluminium by electrolytic process, cryolite is added to reduce the melting temperature of the mixture. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
Question 2
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In the extraction of aluminium the electrolyte is:

A
fused cryolite with felspar

B
fused cryolite with fluorspar

C
pure alumina in molten cryolite with fluorospar

D
pure alumina with bauxite and molten cryolite

Solution

In the extraction of aluminium by electrolytic process alumina $$Al_2O_3$$ is used along with fluorspar and cryolite in molten state.
Question 3
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Zone refining method is used for refining:

A
$$Al$$

B
$$Ge$$

C
$$Cu$$

D
$$Fe$$

Solution

Zone refining is based upon fractional crystallization as the impurity prefers to stay in the melt and on solidification only pure metals solidifies on the surface of the melt.
Metals like $$Si, Ge$$ and $$Ga$$ of high purity are purified by this method.
Question 4
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Which of the following metal is refined by distillation method?

A
Zinc

B
Iron

C
Tin

D
Copper

Solution

Fractional distillation process utilizes the boiling point difference between metal and that of impurity. Using this process, crude zinc containing $$Cd, Fe$$ and $$Pb$$ as impurities can be refined.
Question 5
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Aluminium is obtained by the electrolysis of pure $$Al_{2}O_{3}$$, dissolved in:

A
alumina

B
bauxite

C
cryolite and flourspar

D
feldspar

Solution

Aluminium is obtained by the electrolysis of pure alumina $$(Al_{2}O_{3})$$ dissolved in cryolite $$(Na_3AlF_6)$$ and fluorspar $$(CaF_2)$$. Cryolite and fluorspar lower the melting point of the mixture and increase electrical conductivity.
Question 6
1 / -0

Cryolite is used in the electrolytic extraction of aluminium, because ___________ .

A
it dissolves alumina

B
it dissolves sodium

C
it dissolves aluminium fluoride

D
it decreases the solubility

Solution

In the extraction of aluminium by electrolytic process, alumina $$Al_2O_3$$ is used along with fluorspar and cryolite. Cryolite reduces the melting temperature of the mixture, and also act as solvent to help dissolve $$Al_2O_3$$.
Question 7
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Which of the following technique is used in the manufacture of aluminium from bauxite?

A
Reduction with magnesium

B
Reduction with coke

C
Electrolytic reduction

D
Reduction with iron

Solution

Highly electropositive elements like Na, K, Al, Mg, Ca, Al can't be reduced by Carbon at moderate temperature. At high temperature, the metal combines with carbon to form carbide. So these metals are extracted by electrolysis of their oxides and this process is called electrolytic reduction.
Question 8
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The solubility of impurities in a metal in molten and solid states is different. This is principle involved in the refining of a metal by which of the following methods?

A
Poling

B
Liquation

C
Zone refining

D
Electrolysis

Solution

Zone refining is based upon fractional crystallization as the impurity prefers to stay in the melt and on solidification, only pure metals solidify on the surface of the melt.
In this process, solubility of the impurities in the metal in molten and solid states is different.
Question 9
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Observe the following statements regarding purification of bauxite:
I. During Hall's process, silica is removed as Si (vapour).
II. Bauxite ore contaminated with $$Fe_{2} O_{3}$$ is purified in Baeyer's process.
III. During Serpeck's process, $$AlN$$ is formed.

A
I , II and III are correct

B
Only I and II are correct

C
Only I and III are correct

D
Only II and III are correct
Solution
- Hall-Heroult's process is the electrolysis refining of bauxite ore. $$CO_2$$ is removed as impurities. Thus statement $$I$$ is incorrect.
- The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide).
$$TiO_2, Fe_2O_3, SiO_2$$ exists as impurities in the bauxite ore. All the impurities are removed during this purification process.
Thus statement $$II$$ is correct.
Serpeck's Process:
$$Al_2O_3. 2H_2O + 3C + N_2 \rightarrow 2AlN + 3CO+ 2H_2O$$
$$AlN$$ is formed in the Serpeck's process. Hence III is correct statement.

Option D is correct.
Question 10
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Identify the reaction during electrolytic reduction of alumina at cathode.

A
$$2H_{2}O_{2}\rightarrow O_{2}+4H^{+}+4e^{-}$$

B
$$3F^{-}\rightarrow 3F+3e^{-}$$

C
$$Al^{+3}+3e^{-}\rightarrow Al$$

D
$$2H^{+}+2e^{-}\rightarrow H_{2}$$

Solution

During electrolytic reduction of Alumina,

the reaction at cathode is $$Al^{+3}+3e^{-}\rightarrow Al$$.

Option C is correct.

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General Principles and Processes of Isolation of Elements Test - 18

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General Principles and Processes of Isolation of Elements Test - 18

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Question 1

lower the melting point of alumina

increase the electrical conductivity

minimise the anode effect

remove impurities from alumina

Solution

Question 2

fused cryolite with felspar

fused cryolite with fluorspar

pure alumina in molten cryolite with fluorospar

pure alumina with bauxite and molten cryolite

Solution

Question 3

$$Al$$

$$Ge$$

$$Cu$$

$$Fe$$

Solution

Question 4

Zinc

Iron

Tin

Copper

Solution

Question 5

alumina

bauxite

cryolite and flourspar

feldspar

Solution

Question 6

it dissolves alumina

it dissolves sodium

it dissolves aluminium fluoride

it decreases the solubility

Solution

Question 7

Reduction with magnesium

Reduction with coke

Electrolytic reduction

Reduction with iron

Solution

Question 8

Poling

Liquation

Zone refining

Electrolysis

Solution

Question 9

I , II and III are correct

Only I and II are correct

Only I and III are correct

Only II and III are correct

Solution

Question 10

$$2H_{2}O_{2}\rightarrow O_{2}+4H^{+}+4e^{-}$$

$$3F^{-}\rightarrow 3F+3e^{-}$$

$$Al^{+3}+3e^{-}\rightarrow Al$$

$$2H^{+}+2e^{-}\rightarrow H_{2}$$

Solution

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