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

Total Questions: 50

1. When lead nitrate is mixed with potassium iodine, the precipitate formed is_______. [RRC Group D 26/09/2022 (Afternoon)]

Correct Answer: (d) yellow colour lead iodide
Solution:

Pb(NO₃)₂(lead nitrate) + 2KI (potassium iodide) → PbI₂ (lead iodide) + 2KNO₃ (Potassium nitrate). Double displacement reaction is a type of reaction in which two reactants exchange ions to form two new compounds.
Example - 2NaCl (Sodium chloride) + CaSO₄ (Calcium sulfate) → Na₂SO₄ (Sodium Sulfate) + CaCl₂ (Calcium chloride).

2. Which of the following gases is evolved when limestone undergoes thermal decomposition? [RRC Group D 26/09/2022 (Afternoon)]

Correct Answer: (b) Carbon dioxide
Solution:

Thermal decomposition reaction - A reaction in which a compound breaks down or decomposes on heating. Example: CaCO₃ (Calcium Carbonate) → CaO (Calcium oxide) + CO₂ (carbon dioxide).
Properties of carbon dioxide - Colorless and odourless gas, non-flammable gas, heavier than air, melting point (-56.6°C) ,boiling point (-78.5°C).
Uses - Used as a refrigerant, as a fire extinguisher, promoting the growth of plants in greenhouses and carbonated beverages.

3. Double displacement reaction takes place with: [RRC Group D 26/09/2022 (Evening)]

i) Precipitates are formed.
ii) Evolution of a gas
iii) Change in colour.

Correct Answer: (b) i, ii and iii
Solution:

Double Displacement - A reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds. Example: AB + CD → AD + CB.
Example: Precipitates are formed - AgNO₃ (silver nitrate) + NaCl (Sodium chloride) + NaNO₃ (sodium nitrate), Evolution of a gas - Na₂S(aq) + 2HCl(aq) → 2NaCl(aq) + H₂S(g), Change in colour - 2KI(aq) + Pb(NO₃)₂(aq) → 2KNO₃(aq) + PbI₂(s).

4. A student takes a ribbon and burns it in the presence of oxygen. It changes into magnesium oxide. Which process has occurred? [RRC Group D 26/09/2022 (Evening)]

Correct Answer: (a) Oxidation
Solution:

When metals react with acid, a reactant loses electrons during a reaction. Examples of oxidation are rust and the brown colour of a cut apple. Hydrogenation: Chemical reaction between molecular hydrogen and other compounds and elements.
Uses: food industry, petrochemical industry and the pharmaceutical manufacturing industry. Reduction: It involves a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons.

5. Study the given chemical reaction and find the values of x, y and z, respectively. [RRC Group D 26/09/2022 (Evening)]

x𝐹𝑒 ₛ +y𝐻₂𝑂(g) → 𝐹𝑒₃𝑂₄+ z𝐻₂ (g)

Correct Answer: (c) 3, 4, 4
Solution:

Putting x = 3, y = 4, z = 4. 3Fe(s) + 4H₂O(g) → Fe₃O₄ + 4H₂(g).
It is a single displacement reaction. The equation is balanced.

6. Oxides of which of the following elements CANNOT be reduced by 𝐻₂, CO and C? [RRC Group D 27/09/2022 (Morning)]

Correct Answer: (b) Ca
Solution:

Potassium (K), Sodium (Na), Magnesium (Mg), Calcium (Ca), Aluminum (Al) metals have more affinity for oxygen than carbon and 𝐻₂ . Iron (Fe), zinc (Zn), lead (Pb), and 2 copper (Cu) are moderately reactive elements.

7. Which of the following is an example of a double displacement reaction? [RRC Group D 27/09/2022 (Morning)]

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

Na2SO4 (Sodium Sulphate) + BaCl₂ (Barium Chloride) → BaSO₄ (Barium Sulphate) + 2NaCl (Sodium Chloride). Double Displacement Reaction - A type of reaction where part of one reactant is replaced by part of another reactant. Example - AgNO₃ (Silver Nitrate) + NaCl (Sodium Chloride) → AgCl (Silver Chloride) + NaNO₃ (Sodium Nitrate). FeSO₄ - Iron Sulphate. Fe₂O₃ - Ferric oxide. CaO - Calcium Oxide. Ca(OH)₂ - Calcium Hydroxide.

8. Which product is formed near the cathode in the given chemical reaction? [RRC Group D 27/09/2022 (Afternoon)]

2NaCl(aq) + 2𝐻₂O(l) → 2NaOH(aq) + 𝐻₂ (g) + 𝐶𝑙₂ (g)

Correct Answer: (a) NaOH, 𝐻₂
Solution:

NaOH, H₂ (Hydrogen) at the cathode and Cl₂ (Chlorine) at the anode. NaOH (Sodium hydroxide): used to produce soaps, rayon, paper and petroleum products. Chlorine (Cl, 17): used to disinfect water.
Properties: Greenish-yellow colour, pungent odour, twice as dense as air, belongs to the halogen group, a powerful oxidizing, bleaching and disinfecting agent.

9. The given reaction is an example of a__________. [RRC Group D 27/09/2022 (Afternoon)]

Correct Answer: (b) displacement reaction
Solution:

Single Displacement Reaction: Part of one reactant is replaced by another reactant. Example - 2K (Potassium) + MgCl₂ (Magnesium chloride) → 2KCl (Potassium chloride) + Mg (Magnesium).

10. Identify the substance that is reduced in the following reaction. [RRC Group D 27/09/2022 (Evening)]

ZnO + C → Zn + CO

Correct Answer: (a) ZnO
Solution:

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two elements .
In ZnO (Zinc oxide) + C (Carbon) → Zn (Zinc) + CO (Carbon monoxide), Carbon is oxidised (due to loss of electrons) and Zinc is reduced (due to gain in electrons).