General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 67

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Question 1
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High purity copper metal is obtained by :

A
carbon reduction

B
hydrogen reduction

C
electrolytic reduction

D
thermite reduction

Solution

High purity copper metal is obtained by electrolytic reduction.
Hence, Option "C" is the correct answer.
Question 2
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Which of the following pair is incorrectly matched ?

A
van Arkel method - Zirconium

B
Kroll's process - Titanium

C
Froth floatation - Cerussite

D
Distillation - Zinc

Solution

Froth floatation is not done for Cerrusite because it is not an ore of sulphide.
Hence, Option "C" is the correct answer.
Question 3
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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 what temperature, zinc and carbon have equal affinity for oxygen?

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

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

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

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

Solution

Based on the given diagram the curves of carbon and Zinc can meet at a constant point i.e Temperature 1000 degrees
It can suggest that at this point the carbon and zinc have equal affinity for oxygen
Question 4
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NaCN is sometimes added in the forth flotation process as depressant when ZnS and PbS minerals are expected because:

A
$$Pb (CN)_{2}$$ is precipitated while no effect on ZnS

B
Zns forms soluble complex $$Na_{2}[Zn(CN)_{4}]$$ While PbS forms forth

C
PbS forms soluble complex $$Na_{2}[Zn(CN)_{4}]$$ while ZnS forms forth

D
NaCN is never added in forth floatation process

Solution

Depressant is a substance that is added to suppress the floating characteristic of metal sulphide present as an impurity $$PbS+ ZnS\overset{4NaCN}{\rightarrow}Na_{2}[Zn(CN)_{4}]+PbS$$
Question 5
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Directions For Questions

For a spontaneous reaction, the free energy change must be negative. $$\Delta G = \Delta H - T\Delta S, \Delta H $$ is the enthalpy change during the reaction. T is absolute temperature, and $$\Delta S$$ is the change in entropy during the reaction. Consider a reaction. T is formation of an oxide $$ M+ O_{2} \rightarrow MO$$ Dioxygen is used in the course of this reaction. Gases have a more random structure ( less ordered) than liquid or solids. Consequently gases have a higher entropy than liquids and solids. In this reaction S ( entropy or randomness ) decreases, hence $$\Delta S$$ is negative. Thus, if the temperature is raised then $$T\Delta S$$ becomes less more negative. Thus, the free energy change increases with the increases in temperature. The free energy change that occur when one mole common reactant ( in this case dioxygen) is used may be plotted graphically against temperature for a number of reaction of metals to their oxides. The following plot is called an Ellingham diagram for metal oxide. Understating of Ellingham diagram is extremely diagram is extremely important for the efficient extraction of metals.

...view full instructions

Free energy change of Hg and Mg for the conversion of oxides the slope of $$\Delta G$$ vs. T has been changed above the boiling point of the given metal because :

A
above the boiling point of the given metal the entropy is increased

B
above the boiling point of the metal the entropy is decreased

C
above the boiling point of the metal the entropy change is equal to zero

D
All of these

Solution

Free energy change of Hg and Mg for the conversion of oxides the slope of $$\Delta G$$ vs. T has been changed above the boiling point of the given metal because above the boiling point of the given metal the entropy is increased.

Hence, Option "A" is the correct answer.
Question 6
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Directions For Questions

For a spontaneous reaction, the free energy change must be negative. $$\Delta G = \Delta H - T\Delta S, \Delta H $$ is the enthalpy change during the reaction. T is absolute temperature, and $$\Delta S$$ is the change in entropy during the reaction. Consider a reaction. T is formation of an oxide $$ M+ O_{2} \rightarrow MO$$ Dioxygen is used in the course of this reaction. Gases have a more random structure ( less ordered) than liquid or solids. Consequently gases have a higher entropy than liquids and solids. In this reaction S ( entropy or randomness ) decreases, hence $$\Delta S$$ is negative. Thus, if the temperature is raised then $$T\Delta S$$ becomes less more negative. Thus, the free energy change increases with the increases in temperature. The free energy change that occur when one mole common reactant ( in this case dioxygen) is used may be plotted graphically against temperature for a number of reaction of metals to their oxides. The following plot is called an Ellingham diagram for metal oxide. Understating of Ellingham diagram is extremely diagram is extremely important for the efficient extraction of metals.

...view full instructions

Which of the following elements can be prepared by heating the oxide above $$400^{\circ}C$$ ?

A
Hg

B
Mg

C
Fe

D
Al

Solution
Question 7
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correct statement in the electrolysis of $$Al_{2}O_{3}$$ by Hall-Heroult process is:

A
Cryolite $$Na_{3}[AlF_{5}]$$ lowers the m.pt. of $$Al_{2}O_{3}$$ and increases its electrical conductivity

B
Al is obtained at cathode and $$CO_{2}$$ at anode

C
both (a) and (b) are correct

D
none of the above
Solution
The electrolysis of alumina by Hall and Heroult's process is carried by using a fused mixture of alumina and cryolite along with minor quantities of aluminum fluoride and fluorspar.
The addition of cryolite and fluorspar increases the electrical conductivity of alumina and lowers the fusion temperature.
At cathode $$Al(III)$$ is reduced to $$Al $$metal.
At the anode, alumina reacts with fluorine to liberate oxygen. Oxygen reacts with carbon to form carbon dioxide.
Question 8
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When ZnS and PbS minerals are present together, then NaCN is added to separaye them in the forth floaatation process as a depressant, because:

A
$$Pb (CN)_{2}$$ is precipitated while no effect on ZnS

B
ZnS forms soluble complex $$Na_{2}[Zn(CN)_{4}]$$

C
PbS forms soluble complex $$Na_{2}[Zn(CN)_{4}]$$

D
The cannot be separated by adding NaCN

Solution

$$ZnS+4NaCN\rightleftharpoons 4Na^{+}+[Zn(CN)_{4}]^{-2}+S^{2-}$$
Question 9
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Which of the following substance acts as collector in froth floatation method?

A
Sodium xenate

B
Sodium pyrophosphate

C
Sodium nitroprusside

D
Sodium ethyl xanthate

Solution
Question 10
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Directions For Questions

The Ellingham diagram for an a number of sulphides is shown below.

...view full instructions

Which sulphide occurs to minimum extent in nature

A
$$HgS$$

B
$$H_{2}S$$

C
$$Bi_{2}S_{3}$$

D
$$CS_{2}$$

Solution

As the curve of $$CS_2$$ has a consistent negative slope, it occurs in a minimum extent.
Hence, Option "D" is the correct answer.