General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 55

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Weekly Quiz Competition

Question 1
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$$FeCr_2O_4$$ (Chromite) is a good source of chromium and its compound like $$Na_2CrO_4$$ and $$Na_2Cr_2O_7$$

I. $$FeCr_2O_4 + NaOH + air \longrightarrow (A) + Fe_2O_3$$

II. $$(A) + (B) \longrightarrow Na_2Cr_2O_7$$

III. $$Na_2Cr_2O_7 + X \overset{\triangle}{\longrightarrow} Cr_2O_3$$

IV. $$Cr_2O_3 + Y \overset{\triangle}{\longrightarrow} Cr$$

Compounds (A) and (B) are:

A
$$Na_2CrO_4, H_2SO_4$$

B
$$Na_2Cr_2O_7, HCl$$

C
$$Na_2CrO_6, H_2SO_4$$

D
$$Na_4[Fe(OH)_6], H_2SO_4$$

Solution

Compounds (A) and (B) are $$Na_2CrO_4 \ and \ H_2SO_4$$.

$$FeCr_2O_4\, +\, NaOH\, +\, air\, \rightarrow\, {(A)} {Na_2CrO_4}\, +\, Fe_2O_3$$

$$\underset {(A)} {Na_2CrO_4}\, +\, \underset {(B)} {H_2SO_4}\, \rightarrow\, Na_2Cr_2O_7$$
Question 2
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From the Ellingham diagram, identify the oxide which is reduced by the carbon at highest temperature among the following oxides.

$$MgO,$$ $$CaO,$$ $$TiO_2$$ and $$Al_2O_3$$

A
$$MgO$$

B
$$CaO$$

C
$$TiO_2$$

D
$$Al_2O_3$$
Question 3
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Use the relationship $$\Delta \,G^{\circ}\,=\,- nFE^{\circ}_{cell}$$ to estimate the minimum voltage required to electrolyse $$Al_2O_3$$ in the Hall-Heroult process.
$$\Delta G^{\circ}_{f}(Al_2O_3)\,=\,-1520\,kJ\,mol^{-1}$$
$$\Delta G^{\circ}_{f}(CO_2)\,=\,-394\,kJ\,mol^{-1}$$
The oxidation of the graphite anode to $$CO_2$$ permits the electrolysis to occur at a lower voltage than if the electrolysis reactions were :
$$Al_2O_3\,\rightarrow\,2Al\,+\,3O_2$$.

What is the approximate value of low voltage?

A
2 V

B
3 V

C
4V

D
5V

Solution

Net reaction in Hall-Heroult process is
$$3C\,+\,2Al_2O_3\,\rightarrow\,4Al\,+\,3CO_2$$
Or $$4Al^{3+}\,+\,12e^{-}\,\rightarrow \,4Al,$$
Number of electrons (n) = 12
$$\Delta\,G^{\circ }\,=\,3 \Delta\, G^{\circ }_f (CO_2)\,-\,2 \Delta\,G^{\circ }_f(Al_2O_3)$$
$$=-3\,\times\,394\,-\,2(-1520)$$
$$= 1858\ kJ$$

$$\Delta G^{\circ}\,=\, -nFE^{\circ}_{cell}$$
$$-E^{\circ}_{cell}\,=\, \displaystyle \frac {\Delta G^{\circ}}{nF}\, =\, \displaystyle\frac {1858\,\times\, 1000}{12\, \times\, 96500}$$
$$= 1.60\ V$$
Thus, Hall-Heroult process takes place at lower voltage.

Question 4

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Match column A (process) with column B (electrolyte).

A (process)	B (electrolyte)
(I) Downs Cell	(W) Fused $$MgCl_2$$
(II) Dow sea water	(X) Fused $$Al_2O_3 + Na_3AlF_6$$
(III) Hall-Heroult	(Y) Fused $$KHF_2$$
(IV) Moissan	(Z) Fused 40% NaCl + 60% CaCl$$_2$$

Choose the correct alternative:

I-Z, II-W, III-X, IV-Y

I-X, II-Y, III-Z, IV-W

I-W, II-Z, III-X, IV-Y

I-X, II-Z, III-W, IV-Y

Solution

(1) In Downs cell molten $$MgCl_2$$ is electrolyzed, the electrolyte used in the cell is a fused mixture of 40% NaCl and 60% $$CaCl_2$$.

(II) In Dow process, $$Mg(OH)_2$$ is precipitated from sea-water by slurrying with calcined dolomite and then converting it to $$MgCl_2$$ by reacting with HCl. In Dow sea water process, the electrolyte used is fused $$MgCl_2$$.

(III) In the Hall-Heroult process, the electrolyte used is a fused mixture of $$Al_2O_3$$ and $$Na_3AlF_6$$.

(IV) In Moissan process, the electrolyte used is fused $$KHF_2$$.

The correct match is:
I-Z, II-W, III-X, IV-Y

Question 5
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$$\Delta G$$ vs $$T$$ plot in the Ellingham diagram slopes downward for the reaction.

A
$$Mg + \dfrac {1}{2} O_{2} \longrightarrow MgO$$

B
$$2Ag + \dfrac {1}{2} O_{2} \longrightarrow Ag_2O$$

C
$$C + \dfrac {1}{2} O_{2} \longrightarrow CO$$

D
$$CO + \dfrac {1}{2} O_{2} \longrightarrow CO_{2}$$

Solution

In Ellingham diagram,
higher is the slope higher is the entropy change so
$$\Delta S(C_{(s)} + 1/2 O_{2(g)} \longrightarrow CO_{(g)}) > \Delta S (C_{(S)} + O_{2(g)} \longrightarrow CO_{2(g)}$$
as CO have higher slope.
Also,
Carbon monoxide is a more effective reducing agent than carbon below 983 K but above this temperature the reverse is true.
Question 6
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Directions For Questions

Questions given below are based on the Periodic Table showing different ores/minerals.
Primary mineral sources of metals. The s-block metals occur as chloride, silicates, and carbonates. The d- and p-block metals are found as oxides and sulphides, except for the group 3, metals, which occur as phoshates, and the platinum group metals and gold, which occur in uncombined form. There is no mineral source of technitium (Tc in group 7), a radioactive element that is made in nuclear reactors.

...view full instructions

Elements found in native state are

A
Pb and Bi as they are in p-block

B
Hg and Os as they are in liquid state

C
C and Si as they are non-metals

D
Pt and Au as they are at the bottom of the electrochemical series

Solution

An element is said to exist in native state, if it is found in nature in its elementary form. Pt and Au found as they are at the bottom of the electrochemical series are least reactive among all.
Question 7
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Froth flotation process which is used for the concentration of sulphide ore:

A
is based on the difference in wettability of different minerals

B
uses sodium ethyl xanthate, $$ C_2H_5OCS_2Na$$ as collector

C
uses NaCN as depresent in the mixture of ZnS and PbS when ZnS forms soluble complex and PbS forms froth

D
All of the above are correct

Solution

(A) Froth flotation process used for the concentration of sulphide ore is based on the difference in wettability of different minerals.
The metallic sulfide particles of ore are preferentially wetted by oil and the gangue particles by water.
Thus, the option A is correct.
(B) Collectors such as sodium ethyl xanthate $$C_2H_5OCS_2Na$$ are used. pine oils, fatty acids etc. are also used as collectors.
Thus, the option B is correct.
(C) When the minerals are expected to contain PbS and ZnS, suitable depressants such as naCN are added.
The added NaCN, selectively prevents ZnS from coming to the froth by forming soluble complex $$Na_2[Zn(CN)_4]$$ and PbS is separated along with the froth.
Thus, the option C is correct.
Question 8
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Select correct statement:

A
In the decomposition of an oxide, into oxygen and gaseous metal, entropy increases.

B
Decomposition of an oxide is an endothermic change.

C
To make $$\Delta G^{\circ}$$ negative, temperature should be high enough so that T $$\Delta S^{\circ}\, >\, \Delta H^{\circ}$$.

D
All of the above are correct statements.

Solution

(A) In the decomposition of an oxide, into oxygen and gaseous metal, entropy increases.
This is because the change in the number of moles for the gaseous substances is positive.
Thus, the option A is correct.
(B) Decomposition of an oxide is an endothermic change.
This is because alarge amount of energy must be supplied to break the bonds between metal and oxygen.
Thus, the option B is correct.
(C) $$\Delta G^0 = \Delta H^0-T \Delta S^0$$
When the temperature is sufficiently high, $$T \Delta S^0>\Delta H^0 $$ .
Hence, the value of $$\Delta G^0 $$ will be negative.
Thus, option C is correct.
Thus all the statements are correct.
Question 9
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The chemical process in the production of steel from haematite ore involves ___________.

A
reduction

B
oxidation

C
reduction followed by oxidation

D
oxidation followed by reduction

Solution

The chemical process in the production of steel from haematite ore involves oxidation followed by reduction.
Ferrous oxide is oxidized to ferric oxide.
$$4FeO+O_2 \rightarrow 2Fe_2O_3$$
Ferric oxide is reduced to iron metal.
$$Fe_2O_3+3CO \xrightarrow {400^0C-700^0C} 2Fe+3CO_2$$
Question 10
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Find out B in the given process.

A
$$Na[Al(OH)_4]$$

B
$$NaOH$$

C
$$H_2SO_4$$

D
$$Al_2O_3$$

Solution

By this process, Aluminium is extracted from alumina.

Reaction:

$$Al_2O_3.2H_2O \xrightarrow {conc.\ Na_2CO_3} Na[Al(OH)_4] \xrightarrow {CO_2} Al_2O_3 \xrightarrow {Mix\ with\ Na_3AlF_6} Al$$
A B C D E F

Therefore, B is $$Na[Al(OH)_4]$$

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General Principles and Processes of Isolation of Elements Test - 55

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General Principles and Processes of Isolation of Elements Test - 55

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Question 1

$$Na_2CrO_4, H_2SO_4$$

$$Na_2Cr_2O_7, HCl$$

$$Na_2CrO_6, H_2SO_4$$

$$Na_4[Fe(OH)_6], H_2SO_4$$

Solution

Question 2

$$MgO$$

$$CaO$$

$$TiO_2$$

$$Al_2O_3$$

Question 3

2 V

3 V

4V

5V

Solution

Question 4

I-Z, II-W, III-X, IV-Y

I-X, II-Y, III-Z, IV-W

I-W, II-Z, III-X, IV-Y

I-X, II-Z, III-W, IV-Y

Solution

Question 5

$$Mg + \dfrac {1}{2} O_{2} \longrightarrow MgO$$

$$2Ag + \dfrac {1}{2} O_{2} \longrightarrow Ag_2O$$

$$C + \dfrac {1}{2} O_{2} \longrightarrow CO$$

$$CO + \dfrac {1}{2} O_{2} \longrightarrow CO_{2}$$

Solution

Question 6

Pb and Bi as they are in p-block

Hg and Os as they are in liquid state

C and Si as they are non-metals

Pt and Au as they are at the bottom of the electrochemical series

Solution

Question 7

is based on the difference in wettability of different minerals

uses sodium ethyl xanthate, $$ C_2H_5OCS_2Na$$ as collector

uses NaCN as depresent in the mixture of ZnS and PbS when ZnS forms soluble complex and PbS forms froth

All of the above are correct

Solution

Question 8

In the decomposition of an oxide, into oxygen and gaseous metal, entropy increases.

Decomposition of an oxide is an endothermic change.

To make $$\Delta G^{\circ}$$ negative, temperature should be high enough so that T $$\Delta S^{\circ}\, >\, \Delta H^{\circ}$$.

All of the above are correct statements.

Solution

Question 9

reduction

oxidation

reduction followed by oxidation

oxidation followed by reduction

Solution

Question 10

$$Na[Al(OH)_4]$$

$$NaOH$$

$$H_2SO_4$$

$$Al_2O_3$$

Solution

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