Railway Science (Chemistry-Chemical Reaction)

Total Questions: 50

41. When lead nitrate is heated, lead oxide, oxygen gas and a brownish gray gas are formed. What is that mysterious gas ? [RRC Group D 26/08/2022 (Afternoon)]

Correct Answer: (c) Nitrogen dioxide
Solution:

Lead nitrate on heating undergo thermal decomposition reaction to form a yellow residue of lead oxide, brown fumes of nitrogen dioxide and oxygen. Reaction - 2Pb(NO₃)₂ (Lead nitrate) → 2PbO (Lead oxide) + 4NO₂ (Nitrogen dioxide) + O₂ (Oxygen). Nitrous oxide (Laughing gas - N₂O). Carbon Dioxide (CO₂). Carbon monoxide (CO).

42. In the presence of ultraviolet radiation, silver chloride decomposes into silver and chlorine gas. This is an example of ______. [RRC Group D 26/08/2022 (Evening)]

Correct Answer: (d) Photolytic decomposition reaction
Solution:

Photolytic decomposition reaction - Photolysis is the splitting or decomposition of a chemical compound by means of light energy or photons. Thermal decomposition reaction - activated by thermal energy.
Redox reactions - oxidation-reduction chemical reactions in which the reactants undergo a change in their oxidation states. Double displacement reaction - positive and negative ions of two ionic compounds exchange places to form two new compounds.

43. What type of reaction is the formation of methyl chloride from methane and chlorine gas? [RRC Group D 26/08/2022 (Evening)]

Correct Answer: (b) Substitution reaction
Solution:

Substitution reaction - In which the functional group of one chemical compound is substituted by another group, Example - CH₄ (Methane) + Cl₂ (Chlorine) → CH₃Cl (Chloromethane) + HCl (Hydrochloric Acid).

44. Which of the following reactions would be considered a double displacement reaction ? [RRC Group D 26/08/2022 (Evening)]

Correct Answer: (c) HCI + KOH → KCI + 𝐻₂O
Solution:

Double displacement reaction - 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.

45. Shreya adds some calcium hydroxide in a test tube containing concentrated sulphuric acid. The main product of the reaction will be: [RRC Group D 29/08/2022 (Morning)]

Correct Answer: (b) calcium sulphate
Solution:

The reaction between calcium hydroxide {Ca(OH)2} and concentrated sulphuric acid (H₂SO₄) - Ca(OH)₂(aq) + H₂SO₄(aq) → CaSO₄(s) + 2H₂O(l). This is a very exothermic reaction.
It produces a considerable amount of energy and can easily generate enough energy to cause fires if performed in improper circumstances.

46. Identify the double displacement reaction from the following. [RRC Group D 29/08/2022 (Morning)]

Correct Answer: (d) Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) + 2NaCl (aq)
Solution:

Double displacement Reaction (AB + CD → AD + CB) - in which the positive and negative ions of two ionic compounds exchange places to form two new compounds.
Example - Na₂SO₄ (Sodium sulphate) + BaCl₂ (Barium chloride) → BaSO₄ (Barium Sulphate) + 2NaCl (Sodium chloride).
The other 3 reactions are displacement reactions. Displacement reaction (A + BC → AC + B) - One element takes place with another element in the compound.

47. Which of the statements about the reaction below is/are correct? [RRC Group D 29/08/2022 (Afternoon)]

2ZnO (s) + C (s) → 2 Zn (s) + CO₂ → (g)

l. Zinc is getting reduced
ll. Carbon is getting oxidized
lll. Zinc is getting oxidized
lV. Carbon is getting reduced

Correct Answer: (b) Both I and II
Solution:

The given reaction is : 2ZnO (s) + C (s) → 2 Zn (s) + CO₂ (g). It is a type of Redox reaction i.e. a reaction in which the reduction as well as the oxidation are taking place simultaneously.
Zinc is getting reduced because it loses oxygen and the removal of oxygen is the reduction. Carbon is getting oxidized because oxygen gets added to it and the addition of oxygen is the oxidation.

48. Select the option that correctly indicates which of the following statements are true. [RRC Group D 29/08/2022 (Evening)]

When a strip of zinc metal is placed in copper sulfate solution:
(i) zinc displaces copper from copper sulfate
(ii) the blue color of copper sulfate solution does not fade
(iii) a blue deposit of copper metal is formed on the zinc strip
(iv) it is an example of combination reaction

Correct Answer: (d) i
Solution:

When a strip of zinc metal is placed in copper sulphate solution zinc displaces copper from copper sulphate, and copper sulphate will lose its blue colour and a red brown coating of copper will deposit on zinc, it is an example of displacement reaction (CuSO₄ + Zn → ZnSO₄ + Cu). Displacement reaction - chemical reaction in which a more reactive element displaces a less reactive element from its compound.

49. Which of the following is a property of combustion reaction? [RRC Group D 29/08/2022 (Evening)]

Correct Answer: (b) An element burns in the presence of oxygen.
Solution:

Combustion reaction - an exothermic reaction between substances, usually including oxygen gas and accompanied by the generation of heat, energy, and light (flame).
Reaction of Oxygen with metals and non-metals results in the formation of its oxide. Examples of Combustion - Burning of Wood in the air, Combustion of petrol in a car's engine, and An explosion of hydrogen in air.

50. For the following reaction, balance the chemical equation with state symbols. [RRC Group D 29/08/2022 (Evening)]

C𝑂₂ + 𝐻₂O → 𝐶₆𝐻₁₂𝑂₆ + 6𝑂₂ + 6 𝐻₂O

Correct Answer: (a)
Solution:

6Co₂(g) + 12H₂O(l) → 𝐶₆𝐻₁₂𝑂₆ (Glucose, aq) + 6O₂(g) + 6 H₂O(l), represents Photosynthesis. Carbohydrates are produced by the process of carbon assimilation which is carried on by the combination of water, carbon dioxide, by the application of external energy, light, and chlorophyll along with the involvement of oxygen.