General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 41

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Weekly Quiz Competition

Question 1
1 / -0

An ore of tin containing, $$FeCrO_4$$ is concentrated by:

A
gravity separation

B
magnetic separation

C
forth floatation

D
leaching
Solution
Magnetic separation based on differences in magnetic properties of the ore components.
If either the ore or the gangue is attracted towards the magnetic field, then the separation is carried out by this method.
For example, iron ores are attracted towards the magnet, hence, non–magnetic impurities can be separated from them using magnetic separation.
Here,$$FeCrO_4$$ being an iron ore can be separated by magnetic separation.
Question 2
1 / -0

Forth floatation process of concentration is based on the:

A
preferential wetting properties with the frothing agent and water

B
difference in the specific gravities of gangue and ore particles

C
difference in solubility of ganaue and ore particles in frothing agent and water

D
difference in reactivity of gangue and ore particles with water and frothing agent.
Solution
Froth floatation process method is used for removing gangue from sulphide ores.
In this process, a suspension of the powdered ore is made with water. Collectors and froth stabilizers are added to it.
Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth.
The mineral particles become wet by oils while the gangue particles by water.
Question 3
1 / -0

Lithopone is a mixture of zinc sulphide and barium sulphate. It is used as a paint instead of white lead, because it:

A
does not become black in air

B
is more white

C
is more bright

D
does not become yellow in air

Solution

Lithopone is a mixture of zinc sulphide and $${ BaSO }_{ 4 }$$. It is used as paint instead of white lead, because of doesn't become black in air.
Question 4
1 / -0

For which of the following ores forth floatation method is used for concentration?

A
Haematite

B
Zinc blende

C
Magnetite

D
Carnallite
Solution
- Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water
- Among the given options Zinc blend ($$ZnS$$) is the only sulphide ore and hence Froth floatation process is used for its concentration.
- Hence, option B is the right answer.
Question 5
1 / -0

Study the Ellingham diagram for the formation of some oxides and answer the following question.
At the point of intersection of $$Al_2O_3$$ and $$MgO$$ curves (A), $$\triangle G^0$$ becomes zero for the reaction,

$$\frac{2}{3}Al_2O_3+2Mg \rightarrow + \frac{4}{3} Al$$

Below this point, magnesium can reduce alumina. Although thermodynamically feasible, Al is not used for reduction of $$MgO$$ because:

A
temperature required is very high

B
the yields of metal is very low

C
the value of $$\triangle G^0$$ becomes positive

D
magnesium is not used as reducing agent for any reaction

Solution

Temperatures above the point of intersection of $$Al_2O_3$$ and $$MgO$$ curves, Al can reduce MgO. But the temperature required would be so high that the process will be uneconomic and technology is difficult.
Question 6
1 / -0

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water by using depressants. When a depressant $$NaCN$$ is added to an ore containing $$ZnS$$ and $$PbS$$, what is the correct observation?

A
$$NaCN$$ prevents $$PbS$$ from coming to the froth but allows $$ZnS$$ to come with froth

B
$$NaCN$$ prevents $$ZnS$$ from coming to the froth but allows $$PbS$$ to come with froth

C
$$NaCN$$ prevents frothing of both $$ZnS$$ and $$PbS$$, hence no froth is formed

D
$$NaCN$$ does not act as depressant hence a mixture of $$PbS$$ and $$ZnS$$ is found in the froth
Solution
- Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
- It is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using ‘depressants’.
- In the 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.
Question 7
1 / -0

From the Ellingham graph between Gibb's energy and temperature, out of $$C$$ and $$CO$$ which is a better reducing agent for $$ZnO$$?

A
Carbon

B
$$CO$$

C
Both of these

D
None of these

Solution

$$C$$ is a better reducing agent. It reduces at 1180K but when comes to $$CO$$, it reduces at 1270 K.
Question 8
1 / -0

During the formation of the slag by the reaction of flux and impurities which of the following is an example of acidic and basic flux?
(i) $$FeO + SiO_2\rightarrow FeSiO_3$$
(ii) $$SiO_2+MgO\rightarrow MgO\rightarrow MgSiO_3$$

A
(i) $$SiO_2$$ - Acidic flux (ii) $$MgO$$ - Basic flux

B
(i) $$SiO_2$$ - Basic flux (ii) $$MgO$$ - Acidic flux

C
(i) $$SiO_2$$ - Basic flux (ii) $$MgO$$ - Basic flux

D
(i)$$ SiO_2$$ - Acidic flux (ii) $$MgO$$ - Acidic flux

Solution

i) $$FeO+Si{ O }_{ 2 }\longrightarrow FeSi{ O }_{ 3 }$$
In it $$Si{ O }_{ 2 }$$ is acidic flux and used to remove basic impurities.
ii) $$Si{ O }_{ 2 }+MgO\longrightarrow MgSi{ O }_{ 3 }$$
$$Si{ O }_{ 2 }$$ is acidic impurity. $$MgO$$ is basic flux used to remove $$MgSi{ O }_{ 3 }$$ as slag.
Question 9
1 / -0

The reaction $$Cr_2O_3+2Al\rightarrow Al_2O_3+2Cr(\triangle G^0 = -421 kJ) $$ is thermodynamically feasible due to -ve value of $$\triangle G.$$ Why does this reaction not take place at room temperature?

A
Certain amount of activation energy is essential for thermodynamically feasible reactions also.

B
Due to high melting point of chromium oxide the reaction does not take place.

C
Overall value of $$\triangle G$$ for the net reaction becomes positive.

D
Molecules of $$Cr_2O_3$$ and Al are not oriented properly.

Solution

In thermite process,
$${ Cr }_{ 2 }{ O }_{ 3 }+2Al\longrightarrow { Al }_{ 2 }{ O }_{ 3 }+2Cr+Q$$
It is an exothermic and spontaneous process. It requires more activation energy. At room temperature it does not takes place as activation energy is less.
Question 10
1 / -0

Sulphides ores are converted to oxides before reduction. This is explained on the basis of which of the following?

A
Sulphides cannot be reduced easily while oxides can be reduced easily.

B
Sulphides decompose on reduction hence they are fixed converted to oxides.

C
Sulphide ores have higher melting points than oxides.

D
Oxides are more stable than sulphides hence easy to reduce.

Solution

Sulphides ores are converted to oxides before reduction because sulphides cannot be reduced easily while oxides can be reduced easily.

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General Principles and Processes of Isolation of Elements Test - 41

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General Principles and Processes of Isolation of Elements Test - 41

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Question 1

gravity separation

magnetic separation

forth floatation

leaching

Solution

Question 2

preferential wetting properties with the frothing agent and water

difference in the specific gravities of gangue and ore particles

difference in solubility of ganaue and ore particles in frothing agent and water

difference in reactivity of gangue and ore particles with water and frothing agent.

Solution

Question 3

does not become black in air

is more white

is more bright

does not become yellow in air

Solution

Question 4

Haematite

Zinc blende

Magnetite

Carnallite

Solution

Question 5

temperature required is very high

the yields of metal is very low

the value of $$\triangle G^0$$ becomes positive

magnesium is not used as reducing agent for any reaction

Solution

Question 6

$$NaCN$$ prevents $$PbS$$ from coming to the froth but allows $$ZnS$$ to come with froth

$$NaCN$$ prevents $$ZnS$$ from coming to the froth but allows $$PbS$$ to come with froth

$$NaCN$$ prevents frothing of both $$ZnS$$ and $$PbS$$, hence no froth is formed

$$NaCN$$ does not act as depressant hence a mixture of $$PbS$$ and $$ZnS$$ is found in the froth

Solution

Question 7

Carbon

$$CO$$

Both of these

None of these

Solution

Question 8

(i) $$SiO_2$$ - Acidic flux (ii) $$MgO$$ - Basic flux

(i) $$SiO_2$$ - Basic flux (ii) $$MgO$$ - Acidic flux

(i) $$SiO_2$$ - Basic flux (ii) $$MgO$$ - Basic flux

(i)$$ SiO_2$$ - Acidic flux (ii) $$MgO$$ - Acidic flux

Solution

Question 9

Certain amount of activation energy is essential for thermodynamically feasible reactions also.

Due to high melting point of chromium oxide the reaction does not take place.

Overall value of $$\triangle G$$ for the net reaction becomes positive.

Molecules of $$Cr_2O_3$$ and Al are not oriented properly.

Solution

Question 10

Sulphides cannot be reduced easily while oxides can be reduced easily.

Sulphides decompose on reduction hence they are fixed converted to oxides.

Sulphide ores have higher melting points than oxides.

Oxides are more stable than sulphides hence easy to reduce.

Solution

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