General Principles and Processes of Isolation of Elements Test

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General Principles and Processes of Isolation of Elements Test - 25

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Weekly Quiz Competition

Question 1
1 / -0

NaCN is sometimes added in the froth flotation process as a 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 froth

C
PbS forms soluble complex $$Na_2[Pb(CN)_4]$$ while ZnS forms froth

D
NaCN is never added in froth flotation process

Solution

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 removed along with the froth.
Question 2
1 / -0

Siderite is an ore of:

A
$$Cu$$

B
$$Al$$

C
$$Ag$$

D
$$Fe$$

Solution

Siderite is a mineral composed of iron (II) carbonate ($$FeCO_3$$).

Option D is correct.
Question 3
1 / -0

Which one of the following is the chief ore of copper?

A
Galina

B
Copper pyrite

C
Sphalerite

D
Siderite

Solution

The principle ore of copper is copper pyrite ($$CuFeS_2$$) and copper is extracted from this ore.

Option B is correct.
Question 4
1 / -0

Select correct statement(s) about differentiation floatation.

A
It is used to concentrate mixture of sulphides at different stages

B
Zinc sulphate is used to depress zinc sulphide and PbS forms froth

C
Copper sulphate is used to active depressed lead sulphide and $$O_2$$ is blown to make froth

D
All of the above are correct statements

Solution

In differentiation flotation, zinc sulphate is depresses zinc sulphide and PbS forms froth copper sulphate activate depressed lead sulphide. Froth is made by blowing oxygen. Thus, all the given statements are correct.
Question 5
1 / -0

Oxides of the various metals are converted into metal by heating but not in :

A
$$Ag_2O$$

B
CuO

C
HgO

D
all are correct

Solution

Oxides of various metal oxides are converted into metals on heating but CuO (copper oxide) does not not converted into metal on heating but by reaction with Cu2S.
CuO + Heat$$ \rightarrow$$ no reaction
So, answer is B.
Question 6
1 / -0

In electrolysis of $$Al_2O_3$$ by Hall-Heroult process, _____________.

A
Cryolite $$Na_3[AlF_6]$$ lowers the m.p. of $$Al_2O_3$$ and increases its electrical conductivity

B
Al is obtained at cathode and probably $$CO_2$$ 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 fluorpar increases the electrical conductivity of alumina and lowers the fusion temperature. At cathode Al(III) is reduced to Al metal. At anode, alumina reacts with fluorine to liberate oxygen. Oxygen reacts with carbon to form carbon dioxide.
Question 7
1 / -0

Selection of temperature to carry out a reduction process depends so as to make :

A
$$\Delta G$$ negative

B
$$\Delta G$$ positive

C
$$\Delta H$$ negative

D
$$\Delta H$$ positive

Solution

When the fre energy change $$\Delta G$$ has a negative value, the process becomes spontaneous. Hence, the selection of temperature to carry out a reduction process depends so as to make $$\Delta G$$ negative.
Question 8
1 / -0

Consider following equilibrium
$$3Fe(s)\, +\, C(s)\, \rightleftharpoons\, Fe_3C(s),\quad \Delta H^{\circ}\, >\, 0$$
What is the effect of increasing temperature on this equilibrium?

A
reaction proceeds in forward

B
reaction proceeds in backward

C
no effects

D
none of these

Solution

Forward reaction is endothermic so that formation of cementite ($$Fe_3C$$) is favoured at high temperatures and as we increase temperature, reaction will go forward.

When steel containing $$Fe_3C$$ is cooled slowly, equilibrium is displaced in left hand side and the carbon separates. If the steel is cooled rapidly, equilibrium is not attained and the carbon remains in the form of $$Fe_3C$$.
Question 9
1 / -0

The reduction of an oxide by aluminium is called __________.

A
Ellingham process

B
Goldschmidts aluminothermite process

C
Krolls process

D
Van Arkel process

Solution

The reduction of oxide by aluminum is called Goldschmidt's aluminothermite process.

Aluminium is a strong reducing agent. Due to its strong affinity for oxygen, it can reduce certain metal oxides such as $$Fe_2O_3$$ and $$Cr_2O_3$$ to corresponding metals.

Option B is correct.
Question 10
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

Hall and Heroult's process:

$$2Al_2O_3 + 3C \rightarrow 4Al + 3O_2$$

Cathode : $$Al^{3+} (melt) + 3e^- \rightarrow Al(l)$$

Anode : $$C(s) + O^{2-}(g) (melt) \rightarrow CO(g) + 2e^-$$

$$C(s) + 2O^{2-}(g) (melt) \rightarrow CO_2 (g) + 4e^-$$

The electrolysis of alumina by Hall and Heroult's process is carried by using a fused mixture of alumina ($$Al_2O_3$$) and cryolite ($$Na_3AlF_6$$, sodium hexafluoroaluminate) along with minor quantities of aluminum fluoride ($$AlF_3$$) and fluorspar ($$CaF_2$$). The addition of cryolite and fluorspar increases the electrical conductivity of alumina and lowers the fusion temperature.

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General Principles and Processes of Isolation of Elements Test - 25

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General Principles and Processes of Isolation of Elements Test - 25

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Question 1

$$Pb(CN)_2$$ is precipitated while no effect on ZnS.

ZnS forms soluble complex $$Na_2[Zn(CN)_4]$$ while PbS forms froth

PbS forms soluble complex $$Na_2[Pb(CN)_4]$$ while ZnS forms froth

NaCN is never added in froth flotation process

Solution

Question 2

$$Cu$$

$$Al$$

$$Ag$$

$$Fe$$

Solution

Question 3

Galina

Copper pyrite

Sphalerite

Siderite

Solution

Question 4

It is used to concentrate mixture of sulphides at different stages

Zinc sulphate is used to depress zinc sulphide and PbS forms froth

Copper sulphate is used to active depressed lead sulphide and $$O_2$$ is blown to make froth

All of the above are correct statements

Solution

Question 5

$$Ag_2O$$

CuO

HgO

all are correct

Solution

Question 6

Cryolite $$Na_3[AlF_6]$$ lowers the m.p. of $$Al_2O_3$$ and increases its electrical conductivity

Al is obtained at cathode and probably $$CO_2$$ at anode

Both (a) and (b) are correct

None of the above

Solution

Question 7

$$\Delta G$$ negative

$$\Delta G$$ positive

$$\Delta H$$ negative

$$\Delta H$$ positive

Solution

Question 8

reaction proceeds in forward

reaction proceeds in backward

no effects

none of these

Solution

Question 9

Ellingham process

Goldschmidts aluminothermite process

Krolls process

Van Arkel process

Solution

Question 10

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

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