General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 53

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Question 1
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Directions For Questions

The Ellingham diagram for zinc, magnesium and carbon converting into corresponding oxides is shown above. In the diagram, the points shown are melting and boiling points of zinc and magnesium metals. $$\Delta G^o$$ is a function of temperature for some reactions of extractive metallurgy.

...view full instructions

At temperature $$1000^oC$$, $$\Delta G$$ of the reaction $$ZnO+C\rightarrow Zn+CO$$ is _________.

A
-ve

B
+ve

C
zero

D
nothing can be said

Solution

Both oxides of zinc and carbon, i.e., $$ZnO\: \& \: CO$$ met at $$1000^oC$$ in graph. So, at this temperature, $$\Delta G$$ of the given reaction will be zero.
Question 2
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Which one of the following statements is incorrect?

A
In the aluminothermite process, aluminium acts as reducing agent.

B
Lead is extracted from its chief ore by both carbon reduction and self-reduction.

C
Zinc is extracted from its chief ore by carbon reduction.

D
Extraction of gold involves the leaching of ore with cyanide solution followed by reduction with zinc.

E
In Hall-Heroult process, the electrolyte used is a molten mixture of alumina, sodium hydroxide and cryolite.

Solution

(a) $$Cr_{2}O_{3}+2Al\rightarrow Al_2O_3+2Cr^{3+}$$
(b) $$2PbS+2PbO\rightarrow 2PbO+2SO_{2}$$
$$PbS+2PbO\rightarrow 3Pb+SO_{2}$$ (self reduction)
$$PbO+C\rightarrow Pb+CO$$ (carbon reduction)
(c) $$ZnO+C\rightarrow Zn+CO$$ (carbon reduction)
(d) $$4Au(S)+8CN(aq)+2H_{2}O(aq)+O_{2}(g)\rightarrow 4[Au(CN)_{2}]^{-} (aq)+4OH^{-}(aq)$$ - leaching
$$2[Au(CN]_{2}]^{-}(aq)+Zn(S)\rightarrow 2Au(S)+[Zn(CN)_{4}]^{2-}(aq)$$ - reduction
(e) It is a molten mixture of alumina and cryolite
Question 3
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Which of the above given curves is wrongly presented?

A
$$C\rightarrow CO_2$$

B
$$Pb\rightarrow PbO$$

C
$$Zr\rightarrow ZrO_2$$

D
$$Mg\rightarrow MgO$$

Solution

For the transformation $$Pb\rightarrow PbO$$, the curve is wrongly represented.

Consider the reaction $$2Pb(s) + O_2(g) \rightarrow 2PbO(s)$$

This is the combustion reaction. It is exothermic in nature.

Hence, for this reaction, $$\Delta H $$ is negative.

For the above reaction, $$\Delta n < 0$$. Hence, $$ \Delta S$$ is negative.

At low temperature, $$\Delta G$$ will be negative, as the temperature increases, $$\Delta G$$ value increases and becomes positive.
Question 4
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Directions For Questions

The Ellingham Diagram for a number of metallic sulphides is reproduced below :

...view full instructions

Which occurs to minimum extent in nature?

A
$$HgS$$

B
$$H_2S$$

C
$$Bi_2S_3$$

D
$$CS_2$$

Solution

As at natural temperature $$\triangle G^{\small\circ}$$ of $$CS_2$$ is least negative so it is most unstable and has a minimum extent in nature.
Question 5
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Directions For Questions

Questions given below are based on the given diagram for extraction metallurgy.
The points noted by arrows are the melting and boiling points of the metals zinc and magnesium. $$\Delta G^{\small\circ}$$ is a function of temperature for some reactions and extractive metallurgy.

...view full instructions

At what approximate temperature, zinc and carbon have equal affinity for oxygen?

A
$$1000^{\small\circ}C$$

B
$$1500^{\small\circ}C$$

C
$$500^{\small\circ}C$$

D
$$1200^{\small\circ}C$$

Solution

As both oxides met at $$1000^oC$$ in the graph so at this temperature both $$C$$ and $$Zn$$ have an equal affinity with oxygen.
Question 6
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Which of the above metal oxide has the minimum thermal decomposition temperature?

A
$$CaO$$

B
$$FeO$$

C
$$ZrO_2$$

D
$$MgO$$

Solution

$$ZrO_2$$ has the minimum thermal decomposition temperature, as it crosses zero $$\Delta G$$ line at minimum temperature as shown in the Ellingham diagram.

Option C is correct.
Question 7
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Directions For Questions

The Ellingham diagram for zinc, magnesium and carbon converting into corresponding oxides is shown below :

...view full instructions

To make the following reduction process spontaneous, temperature should be:

$$ZnO + C \longrightarrow Zn + CO$$

A
$$1000^{\small\circ}C$$

B
$$>1000^{\small\circ}C$$

C
$$<500^{\small\circ}C$$

D
$$<1000^{\small\circ}C$$

Solution

Above $$ 1000^oC$$, $$ZnO$$ in the graph is above $$CO$$ graph. So, above this temperature, the difference between the free energy of both will be negative and hence the reaction will be spontaneous.
Question 8
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Directions For Questions

The Ellingham diagram for zinc, magnesium and carbon converting into corresponding oxides is shown below :

...view full instructions

At $$1100^{\small\circ}C$$, which reaction is spontaneous to a maximum extent?

A
$$MgO + C \rightarrow Mg + CO$$

B
$$ZnO + C \rightarrow Zn + CO$$

C
$$MgO + Zn \rightarrow Mg + ZnO$$

D
$$ZnO + Mg \rightarrow MgO + Zn$$

Solution

Any metal will reduce oxide of other metals which lie above it in the Ellingham diagram because free energy change will became more negative and as difference increases more energy will be released and reaction will be more spontaneous.
Question 9
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Directions For Questions

The Ellingham diagram for zinc, magnesium and carbon converting into corresponding oxides is shown above. In the diagram, the points shown are melting and boiling points of zinc and magnesium metals. $$\Delta G^o$$ is a function of temperature for some reactions of extractive metallurgy.

...view full instructions

To make the following reduction process spontaneous, temperature should be
$$ZnO+C\xrightarrow {\Delta} Zn+CO$$

A
$$< 1000^oC$$

B
$$ > 1000^oC$$

C
$$< 500^oC$$

D
$$> 500^oC$$ but $$ < 1000^oC$$

Solution

In the Ellingham diagram, the curve which lies below act as a reducing agent.
Above $$ 1000^oC$$, the curve of $$ZnO$$ lies above $$CO$$ as shown in graph. So, above this temperature, the difference between free energies of both will be negative and reaction will be spontaneous.
Question 10
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Which of the above given metal oxides can be reduced by $$Fe$$ (reducing agent) to its respective metal at temperature $$T_1$$?

A
$$ZrO_2$$

B
$$CaO$$

C
$$MgO$$

D
None of the above

Solution

Any metal will reduce oxide of other metals which lie above it in the Ellingham diagram because free energy change will become more negative.
So, only Zr can be reduced by Fe.