Chemistry (Part-I) (UPSC)

31. Consider the following statements: [1998]

Coke is one of the materials of the charge added to blast furnace for the production of steel/iron. Its function is to :

1. act as the reducing agent.

2. remove silica associated with the iron ore.

3. function as fuel; to supply heat.

4. act as an oxidizing agent.

(a) 1 and 2 are correct
(b) 2 and 4 are correct
(c) 1 and 3 are correct
(d) 3 and 4 are correct

Correct Answer: (c) 1 and 3 are correct

Solution:This statement 1 is correct. Coke primarily consists of carbon, which reacts with the oxygen in the iron ore (hematite, Fe:Os) to reduce it to iron. The carbon in coke forms carbon monoxide (CO) which is a strong reducing agent that reduces iron oxides to iron.

Chemical equations involved in process are following:

2C(s) + O2(g)→ 2CO(g)

FeO(s) + CO(g) → Fe(s) + CO₂(g)

Fe₂O, +3CO(g)→ 2Fe(s) + 3CO₂(g)

The removal of silica (SiOs) is typically achieved by adding limestone (CaCO3), not coke. The limestone decomposes to form calcium oxide (CaO), which then reacts with silica to form calcium silicate (slag). Thus statement 2 is not correct This statement 3 is correct. Coke serves as a fuel to generate the high temperatures required in the blast furnace. The combustion of coke provides the necessary heat for the reduction reactions and the melting of iron.

Thus, the correct statements are 1 and 3.

32. Which one of the following metals does not form amalgam? [1998]

(a) Zinc
(b) Copper
(c) Magnesium
(d) Iron

Correct Answer: (d) Iron

Solution:Amalgam is an alloy consisting of mercury and any other element. Iron being exceptional in nature not form amalgam with mercury. That's why mercury is stored in vessels made up of iron. Small quantities of an iron amalgam have, however, been formed by immersing sodium amalgam (containing 1 percent sodium) in a clear, saturated solution of ferrous sulphate. While rest three options zinc,copper and magnesium combine with mercury to form there respective amalgam.

33. The following two Items consist statements. One labeled as the 'Assertion (A)' and the other as "Reason (R). You have to answer these items using the code given below: [1998]

Assertion (A): Sodium metal is stored under kerosene.

Reason (R): Metallic sodium melts when exposed to air.

(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Correct Answer: (c) A is true but R is false

Solution:Sodium metal is generally kept inside kerosene oil because of its extreme reactive nature. In open air it reacts violently and burns vigorously to form sodium oxide.

The presence of sodium ions in a salt can be determined by the color of a flame-Na turns flame yellow.

34. The following two Items consist statements. One labeled as the 'Assertion (A)' and the other as "Reason (R). You have to answer these items using the code given below: [1999]

Assertion (A): To dilute sulphuric acid, acid is added to water and not water to acid.

Reason (R): Specific heat of water is quite large.

(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Correct Answer: (a) Both A and R are true and R is the correct explanation of A

Solution:Sulphuric acid (H₂SO₄) reacts very vigorously with water. in a highly exothermic reaction. Thus if you add water to concentrated sulfuric acid, it can boil and you may get a nasty acid burn. That's why for dilution, acid is added to water not water to acid as specific heat of water is quite large and it can absorb large quantity of heat produced by sulphuric acid Moreover water is less dense than sulphuric acid, so if you pour water on the acid, the reaction occurs on top of the liquid. If you add the acid to the water, it sinks and any wild and crazy reactions have to get through the water or beaker to get to you.

Chemistry (Part-I) (UPSC)

31. Consider the following statements: [1998]

32. Which one of the following metals does not form amalgam? [1998]

33. The following two Items consist statements. One labeled as the 'Assertion (A)' and the other as "Reason (R). You have to answer these items using the code given below: [1998]

34. The following two Items consist statements. One labeled as the 'Assertion (A)' and the other as "Reason (R). You have to answer these items using the code given below: [1999]

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