General Principles And Process Of Isolation Of Elements(11th And 12th > Chemistry ) Questions and answers for exam Preparation

11th And 12th > Chemistry

GENERAL PRINCIPLES AND PROCESS OF ISOLATION OF ELEMENTS MCQs

Total Questions : 15 | Page 1 of 2 pages

Which of the following statements is true about magnetic separation?

It is used when only ores are magnetic in nature.
It is used when only impurities are magnetic in nature
It is used when both ores and impurities are magnetic in nature.
It is used when either ore or impurities are magnetic in nature.

Discuss Question

Answer: Option D. -> It is used when either ore or impurities are magnetic in nature.
:
D
Electromagnetic separation is applicable when either the ore particles or the impurities are magnetic (attracted by a magnet) in nature. Electromagnets present in a rotor attracts magnetic particles forming a separate heap from non-magnetic particles.

Question 2.

Gravity separation is generally applicable for heavier ores such as Haematite and Cassiterite.

True
False

Discuss Question

Answer: Option A. -> True
:
A

Gravity separation also known as hydraulic washing is based on the differences in weight between the gangue and the metal. In general, the metal particles of the ore are heavier than the impurities. So we use the principle of gravity separation to separate the two.
Finely pulverized (powdered) ore is treated with a stream of water such that the lighter gangue particles are washed away leaving behind the heavier ore particles. This is particularly applicable for heavier ore like Cassiterite and Haematite.

Question 3.

Which of the following statements are not true with respect to the production of iron?

The oxide ore is primarily reduced to iron by solid coke.
The oxide ore reduced largely by carbon monoxide.
Major silica impurities are removed as calcium silicate slag.
The silicate slag is used in manufacture of cement.

Discuss Question

Answer: Option A. -> The oxide ore is primarily reduced to iron by solid coke.
:
B, C, and D
During the production of iron, the oxide ore is predominantly reduced to iron by CO (carbon monoxide) and not by coke. In the reduction zone, the reduction takes place between 250

^{0} C

– 700

^{0} C

. In this temperature range, CO is a better reducing agent than carbon. The reaction takes place as follows:

${Fe}_{2} O_{3} (s) + 3 CO(g) \to 2 Fe(l) + 3 {CO}_{2} (g)$
The silica impurities formed during the production of iron are removed as calcium silicate slag on reaction with calcium oxide. The reaction takes place as follows:
$CaO (s) + {SiO}_{2} (s) \to {CaSiO}_{3} (s) (Slag)$
This silicate slag is used in the manufacturing of cement.

Question 4.

When copper pyrite is roasted in excess of air, a mixture of $C u_{2} S$ and $F e O$ are formed. FeO is present as impurity. This can be removed as slag during Smelting. The flux added to form slag is

Silica which is an acidic flux
Limestone, which is a basic flux
$S i O_{2}$ which is a basic flux
CaO which is a basic flux

Discuss Question

Answer: Option A. -> Silica which is an acidic flux
:
A

FeO (Basic gangue) impurity is mixed with $S i O_{2}$ (acidic flux) to form a fusible slag

$F e O$ $+ S i O_{2}$ $\to$ $F e S i O_{3}$

(slag)

Question 5.

While your siblings are eagerly anticipating their first batches of Gold and diamond, you are still yet to get a single gram of copper! Armed with the know-how of extracting copper, you smelt the calcine from the roasting process in a blast furnace. What is the smelt composed of?

Pure Cu metal
Crude Cu metal
$C u_{2} S$ and FeS
Matte Copper

Discuss Question

Answer: Option C. ->

C u_{2} S

and FeS
:
C and D

The roasted ore is mixed with Silica and powdered coke (to deter the oxidation of FeO to $F e_{2} O_{3}$ so that FeO could be removed as $F e S i O_{3}$ )

FeO + $S i O_{2}$ $\to$ $F e S i O_{3}$

The temperature is high enough to melt the slag. Below the layer of slag is molten mass known as Copper Matte. It consists of $C u_{2} S$ and FeS

Question 6.

In Bayer’s leaching process, the siliceous impurities $(S i O_{2})$ are filtered out immediately after leaching with NaOH – True or False?

True
False
$C u_{2} S$ and FeS
Matte Copper

Discuss Question

Answer: Option B. -> False
:
B

Red Bauxite contains $A l_{2} O_{3} .2 H_{2} O$ $+ F e_{2} O_{3}$ (major impurity) + $S i O_{2}$ $+ T i O_{2}$

After calcination, organic matter, volatile substances and moisture are removed. The calcine is then leached with 45 % NaOH solution at about $150^{\circ} C$ where

Note that only $T i O_{2}$ and $F e_{2} O_{3}$ are filtered out.

Question 7.

In the commercial electrochemical process for Aluminium extraction, the electrolyte used is:

$A l (O H)_{3}$ in NaOH
An aqueous solution of $A l_{2} (S O_{4})_{3}$
A molten mixture of $A l_{2} O_{3}$ & $N a_{3} A l F_{6}$
A molten mixture of $A l_{2} O_{3}$ & $A l (O H)_{3}$

Discuss Question

Answer: Option C. -> A molten mixture of

A l_{2} O_{3}

N a_{3} A l F_{6}

:
C

In the electrolytic extraction of Aluminium, purified alumina is mixed with $N a_{3} A l F_{6}$ and $C a F_{2}$ . Cryolite $(N a_{3} A l F_{6})$ helps dissolve Alumina and lowers the melting point of this mix to about 1050 $^{\circ} C$ . Pure Alumina melts at about 2100 $^{\circ} C$ . $C a F_{2}$ is added to enhance the conductivity.

As shown in the above image, the surface on the inside of the steel case is coated with a graphite lining, which acts as the cathode. The electrolyte is a molten mixture of cryolite, molten Alumina and $C a F_{2}$ .

Question 8.

For a thermodynamically spontaneous process the change in free energy is __.

Discuss Question

Answer: Option C. -> A molten mixture of

A l_{2} O_{3}

N a_{3} A l F_{6}

A spontaneous process is one that needs no intervention from outside. It is also called a irreversible reaction. It releases free energy and moves to a lower, thermodynamically more stable state. The change in free energy is negative.

Question 9.

Which of the following pair of metals is purified by van Arkel method?

Ga & In
Ag & Au
Zr & Ti
Ni & Fe

Discuss Question

Answer: Option C. -> Zr & Ti
:
C

van Arkel Method: The impure metal (Zr and Ti) are converted to a volatile compound, impurities being unaffected. The formed pure volatile compound is decomposed to get the pure metal. Hence this is a method to obtain ultra pure metal by refining. Hf & Si can also be purified by van Arkel method.

Question 10.

Of the given options, choose the combination that contains metals whose ores are most appropriate for roasting. In other words, Sulphide ores are common for which kind of metals?