Railway Science (Chemistry-Chemical Reaction) (Part-II)

Total Questions: 50

11. Which gases evolve during complete decomposition of ferrous sulphate crystals? [RRC Group D 01/09/2022 (Evening)]

Correct Answer: (a) Both SO₂ and SO₃
Solution:

2FeSO₄ → Fe₂O₃ + SO₂ + SO₃ is the balanced equation for decomposition of ferrous sulphate. Decomposition reactions are processes in which chemical species break up into simpler parts. Usually, decomposition reactions require energy input.

12. Identify the double displacement reaction from the following. [RRC Group D 02 /09/2022 (Morning)]

(i) 2AgCl(s) → 2Ag(s) + Cl₂ (g)
(ii) Mg (s) + 2HCI (aq) → MgCl₂ (aq) + H₂(g)
(iii) 2KBr (aq) + Bal₂ (aq) → 2KI (aq) + BaBr₂ (s)
(iv) Pb(s) + CuCl₂(aq) → PbCl₂ (aq) + Cu(s)

Correct Answer: (d) (iii)
Solution:

Double displacement - a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds. The double-displacement reaction generally takes the form of AB + CD → AD + CB where A and C are positively-charged cations, while B and D are negatively-charged anions.

13. Which of the following statements about double displacement reactions is correct? [RRC Group D 02/09/2022 (Afternoon)]

Correct Answer: (a) An exchange of ions between two reactants.
Solution:

Double displacement is a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds. Equation - AB + CD → AD + CB .
Example - 2NaCl (Sodium Chloride) + CaSO₄ (Calcium Sulphate) → Na₂SO₄ (Sodium sulphate) + CaCl₂ (Calcium chloride).

14. In the reaction Mn𝑂₂ + 4HCl → MnC𝑙₂ + 2𝐻₂ O + C𝑙₂ : [RRC Group D 02/09/2022 (Evening)]

Correct Answer: (a) M𝑛𝑂₂ is reduced to MnC𝑙₂
Solution:

When a reactant loses electrons during a reaction, it is called oxidation. When a reactant accumulates electrons during a reaction, it is called reduction. In the reaction M𝑛𝑂₂ + 4HCl → MnC𝑙₂ + 2𝐻₂O + C𝑙₂, MnO₂ →  is the oxidizing agent and HCl is the reducing agent.

15. Which of the following reactions is NOT an example of a displacement reaction? [RRC Group D 02/09/2022 (Evening)]

Correct Answer: (b) 2AgBr(s) → 2Ag(s) + B𝑟₂ (g)
Solution:

A displacement reaction is the one wherein the atom or a set of atoms is displaced by another atom in a molecule. For instance, when iron is added to a copper sulphate solution, it displaces the copper metal. A + B - C → A - C + B. The above equation exists when A is more reactive than B.

16. Consider the following chemical reaction. [RRC Group D 05/09/2022 (Morning)]

CO(g) +2𝐻₂ (g) → P  Predict the product (P) of this reaction.

Correct Answer: (b) C𝐻₃OH
Solution:

When one mole of carbon monoxide gas reacts with 2 moles of hydrogen it gives methanol.

17. What is the product of the following combination reaction ? [RRC Group D 05/09/2022 (Morning)]

S𝑂₃ + 𝐻₂O → ?

Correct Answer: (a) 𝐻₂SO₄
Solution:

When sulphur trioxide reacts with water it gives rise to sulphuric acid.

18. Reactions in which there is an exchange of ions between the reactants are called: [RRC Group D 05/09/2022 (Morning)]

Correct Answer: (d) double displacement reactions
Solution:

Exchange reactions - chemical reactions in which the anions and cations of the reactants exchange their positions in the products.
Displacement reaction - chemical reaction in which a more reactive element displaces a less reactive element from its compound.
Precipitation reactions occur in an aqueous solution where two ionic bonds combine, resulting in the formation of an insoluble salt called precipitates.

19. The method of balancing a chemical equation is called: [RRC Group D 05/09/2022 (Afternoon)]

Correct Answer: (a) hit and trial method
Solution:

In this method of balancing chemical equations, experiments are carried out by using the least whole number coefficient to balance the chemical equation. Example - When hydrogen gas reacts with oxygen, a water molecule is formed.
A balanced equation - An equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products.

20. In the following chemical reaction, which chemical species is getting oxidized ? [RRC Group D 05/09/2022 (Afternoon)]

CuO + H₂→ Cu + H₂O

Correct Answer: (d) H₂
Solution:

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. In redox reaction the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron. In the reaction : CuO + H₂ ⟶Cu + H₂O. H₂ is oxidized since it has lost electrons and Cu is reduced since it has gained electrons.