General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 29

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Weekly Quiz Competition

Question 1
1 / -0

The metal oxide which cannot be reduced to metal by carbon is _________.

A
$$ZnO$$

B
$$Fe_2O_3$$

C
$$PbO$$

D
$$Al_2O_3$$

Solution

Reduction of the oxide with carbon at high temperature is known as smelting. The oxides of less electropositive metals like Pb, Zn, Fe, Sn, Cu etc. are reduced by strongly heating them with coal or coke, in the blast furnace.
So among the given options only $$Al_2O_3$$ cannot be reduced by carbon.

Hence, the correct option is $$C$$
Question 2
1 / -0

Which of the given metal oxides is having minimum thermal decomposition temperature?

A
CaO

B
FeO

C
PbO

D
MgO

Solution

$$PbO$$ has the minimum thermal decomposition temperature, as it crosses zero $$\Delta G$$ line at minimum temperature.
Question 3
1 / -0

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out _______________.

A
in the presence of NaCl

B
in the presence of fluorite

C
in the presence of cryolite which forms a melt with lower melting temperature

D
in the presence of cryolite which forms a melt with higher melting temperature

Solution

Correct Answer: Option C

Explanation:

Metallurgy of aluminum is carried out by the Hall-Heroult process.

Cryolite $$(Na_{3}AlF_{6})$$ acts as a solvent for Aluminum oxide.

It lowers the melting point of the ore and also increases conductivity to ease the electrolysis.
Question 4
1 / -0

Which of the following metal's oxide can be reduced by Fe as reducing agent at temperature $$T_1$$?

A
Pb

B
Ca

C
Mg

D
None of these

Solution

At $$T_1$$ temperature, $$\Delta G_f$$ of $$FeO$$ is more negative than that of $$PbO$$. So, $$PbO$$ can be reduced by $$Fe$$ as reducing agent at temperature $$T_1.$$
Question 5
1 / -0

Which one of the above oxidation curve is wrongly presented in the given Gibbs free energy vs temperature graph ?

A
$$C \rightarrow CO_2$$

B
$$Ti \rightarrow TiO_2$$

C
$$Pb \rightarrow PbO$$

D
$$Mg \rightarrow MgO$$

Solution

$$Ti(s) + \cfrac{1}{2}O_{2(g)} \xrightarrow[]{\Delta} TiO_2(s)$$

By increasing temperature,

According to $$\Delta G = \Delta H - T\Delta S, \ \Delta G$$ for formation of $$TiO_2$$ will move toward +ve value.
Question 6
1 / -0

Lead obtained from galena ore (PbS) by air reduction or carbon reduction process contains base metal (Cu, Bi, As, Sn, Zn) as impurities. Gelatin acts as an addition agent in the electrolysis of Pb. In the presence of gelatin, Pb becomes :

A
hard and brittle

B
soft and rubbery

C
smooth and uniform

D
only brittle

Solution

Lead obtained contains impurities like $$Cu, Sb, Sn, As, Ag, Au, etc.$$ which make it hard. During electrolytic refining of lead, the electrolyte $$(PbSiF_6+H_2SiF_6)$$ is mixed with a little gelatin. Gelatin is added for smooth and uniform deposition of lead in this process.

Hence, the correct option is (C).
Question 7
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(i) Metals can be recovered from their ores by chemical methods.

(ii) High purity metals can be obtained by zone refining method.

Which one is true /false.

A
(i) is true and (ii) is false

B
(ii) is true and (i) is false

C
(i) and (ii) are true

D
(i) and (ii) are false

Solution

(i) Many metals occur in nature as oxides, carbonates, sulphides which can be calcined or roasted. Then, they can be further treated chemically to get the metal.
(ii) Elements such as Si, Ge, Ga, etc., which are used as semiconductors, are refined by zone refining method. Highly pure metals arc obtained. The method is based on the difference in solubility of impurities in molten and solid state of the metal. A movable heater is fitted around a rod of the impure metal. The heater is slowly moved across the rod. The metal melts at the point of beating and as the heater moves on from one end of the rod to the other end, the pure metal crystallizes, while the impurities pass on to the adjacent molten zone.
Question 8
1 / -0

Pb is a very important element of carbon family. It forms a number of compounds which are very useful in industries. The process of removal of base metals (Cu, Sn, Bi, As) from lead is called:

A
softening process

B
liquation

C
parke's process

D
cupellalion

Solution

For the removal of base metals the impure bullion is charged to a softening furnace whereby oxidation these elements form drosses or slags and, with some lead, are skimmed from the bath. This is the softening process.
Question 9
1 / -0

The better reducing agent at $$7100^oC$$ is:

A
$$CO$$ (Ellingham diagram)

B
Coke

C
Both are equal

D
None of these

Solution

Ellingham diagram is a graph between $$\Delta G^o$$ and temperature values which determines the spontaneity of a reaction. At $$7100^oC, $$ $$CO$$ acts as better reducing agent by seeing the diagram
Question 10
1 / -0

NaCN used in the froth flotation method for the purification of ore is:-

A
$$ZnS$$ which contain $$PbS$$

B
$${Cu_2 S}$$ which contain $${Fe_2 S_3}$$

C
$$PbS$$ which contain $$ZnS$$

D
$$PbS$$ which contain $${SiO_2}$$

Solution

FROTH FLOATATION PROCESS - This method is used when a higher ore contains impurities with higher density. This method is used for the concentration of Sulphide ores (e.g.: Copper pyrites, iron pyrites, Galena, Zinc blende etc.,)

In this process, collectors and froth stabilisers are added.
Collectors - (e.g., pine oils, fatty acids, xanthates, etc.); Froth Stabilisers - (e.g., cresols, aniline)

The mineral particles become wet by oils while the gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles.

Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants'. Example: In case of an ore containing $$ZnS$$ and $$PbS$$, the depressant used is $$NaCN$$. It selectively prevents $$ZnS$$ from coming to the froth but allows $$PbS$$ to come with the froth.

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General Principles and Processes of Isolation of Elements Test - 29

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General Principles and Processes of Isolation of Elements Test - 29

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Question 1

$$ZnO$$

$$Fe_2O_3$$

$$PbO$$

$$Al_2O_3$$

Solution

Question 2

CaO

FeO

PbO

MgO

Solution

Question 3

in the presence of NaCl

in the presence of fluorite

in the presence of cryolite which forms a melt with lower melting temperature

in the presence of cryolite which forms a melt with higher melting temperature

Solution

Question 4

Pb

Ca

Mg

None of these

Solution

Question 5

$$C \rightarrow CO_2$$

$$Ti \rightarrow TiO_2$$

$$Pb \rightarrow PbO$$

$$Mg \rightarrow MgO$$

Solution

Question 6

hard and brittle

soft and rubbery

smooth and uniform

only brittle

Solution

Question 7

(i) is true and (ii) is false

(ii) is true and (i) is false

(i) and (ii) are true

(i) and (ii) are false

Solution

Question 8

softening process

liquation

parke's process

cupellalion

Solution

Question 9

$$CO$$ (Ellingham diagram)

Coke

Both are equal

None of these

Solution

Question 10

$$ZnS$$ which contain $$PbS$$

$${Cu_2 S}$$ which contain $${Fe_2 S_3}$$

$$PbS$$ which contain $$ZnS$$

$$PbS$$ which contain $${SiO_2}$$

Solution

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