Isolation of Elements Test 5

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Isolation of Elements Test 5

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Question 1
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Only One Option Correct Type
Direction : This section contains 9 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct.
Q.
Ellingham diagram represents a graph of

A
ΔG vsT

B
ΔG° vs T

C
ΔS° vs T

D
ΔG vs P

Solution

Eilingham diagram represents a graph of ΔG° vs T.
Question 2
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ΔG° vsT plot in the Ellingham diagram slopes down for the reaction.

A

B

C

D

Solution

In the case of carbon reacting with dioxygen.

two volumes of CO for every one volume of dioxygen used. Thus, ΔS is positive and hence ΔG becomes increasilngly negative as temperature increases. Consequently the line on Eilingham diagram slope downwards.
Question 3
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The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of the slag.

A
Fe₂O₃ (s) + 3CO (g) → 2 Fe (l) +3CO₂ (g)

B
CaCO₃ (s) → CaO (s) + CO₂ (g)

C
CaO (s) +SiO₂ → CaSiO₃ (s)

D
2C (s) + O₂ (g) → 2 CO(g)

Solution

A slag is an easily fusible material which is formed when gangue still present in the roasted or the calcined ore combines with the flux. For example, in the metallurgy of iron, CaO (flux) combines with silica gangue to form easily fusible calcium silicate (CaSiO₃) slag.
CaO + SiO₂ → CaSiO₃ (slag)
Question 4
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Which metal has a greater tendency to form metal oxide?

A
Cr

B
Fe

C
Al

D
Ca

Solution

Because the change in free energy i.e. ΔG is highly negative for this reaction,
Question 5
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The main reaction occurring in blast furnace during the extraction of iron from haematite is

A
Fe₂O₃ + 3CO → 2Fe + 3CO₂

B
FeO + SiO₂ → FeSiO₃

C
Fe₂O₃ + 3C → 2Fe + 3CO

D
CaO + SiO₂ → CaSiO₃

Solution

3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂
Fe₃O₄ + CO → 3FeO + CO₂
FeO + CO → Fe + CO₂
Question 6
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Consider the following reactions at 10000° C,
Then choose the correct statement from the following.

A
Zinc can be oxidised by CO

B
ZnO can be reduced by CO

C
ZnO can be reduced by C

D
None of the above

Solution

Because the ΔG° of the formation of CO is more negative than that of ZnO at 10000°C.
Question 7
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According to Ellingham diagrams the oxidation reaction of carbon and carbon monoxide may be used to reduce which one of the following oxides at the lowest temperature?

A
Al₂O₃

B
ZnO

C
MgO

D
Cu₂O

Solution

Because ΔG° for reductions of rest three oxides [Al₂O₃, ZnO and MgO] are less negative than that of Cu₂O at lower temperature.
Question 8
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The minimum voltage required to electrolyse alumina in the Hall-Heroult process is [Given, (Al₂O₃) = - 1520 kJ/mol and (CO₂) = 394 k J/mol]

A
1.575

B
1.60 V

C
1.312 V

D
-2.62 V

Solution

In Hall - Heroult process the following reactions occur
Question 9
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Based on the given information (CaO) = - 604.2 kJ/mol and (Al₂O₃) = - 1582 kJ/mol, which of the following is feasible?

A
3CaO + 2AI → AI₂O₃ + 3C

B
3Ca + AI₂O₃ → 2AI + 3CaO

C
Both (a) and (b)

D
None of the above

Solution

3Ca + Al₂O₃→ 2AI + 3CaO
ΔG°= 3 x(CaO) -(Al₂O₃)
= 3 x (-604.2)-(-1582)
= -1812 + 1582 = -230 kJ
ΔG° is negative. Hence, this reaction is feasible.
Question 10
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Matching List Type
Direction : Choices for the correct combination of elements from Column I and Column II are given as options (a), (b), (c) and (d), out of which one is correct.
Q.
Match the Column I with Column II and mark the correct option from the codes given below.

A

B

C

D

Solution

(i) → (q), (ii) → (r), (iii) → (s), (iv) → (p)
Question 11
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Match the Column I with Column II and mark the correct option from the codes given below.

A

B

C

D

Solution

(i) → (r,t), (ii) → (p), (iii) → (s), (iv) → (q)
Question 12
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Statement Type
Direction : This section is based on Statement I and Statement II. Select the correct answer from the codes given below.
Q.
Statement I : Carbon is good reducing agent for sulphides.
Statement II : Carbon is poor reducing agent for iron oxide.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect

Solution

Carbon is a good reducing agent for oxides, it is a poor reducing agent for sulphides. The reason why carbon reduces so many oxides at elevated temperature is that the ΔG°/T line for CO has a negative slope. There is no compound as analogous to CO with a steep negative ΔG°/T line. Thus sulphides are normally roasted in air to form oxides before reducing with carbon
2 MS + 3O₂→ 2MO + 2SO₂
Question 13
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Statement I : Carbon can reduce Fe₂O₃ to Fe at a temperature below 983 K.
Statement II : Iron has higher affinity toward oxygen than carbon.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect

Solution

Below 983 K iron having higher affinity towards oxygen than carbon, carbon cannot reduce Fe₂O₃ to Fe.