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

Total Questions: 50

1. In the given reaction, reduction of which substance takes place? [RRC Group D 11/10/2022 (Afternoon)]

𝐹𝑒₂𝑂₃ (𝑠) + 2𝐴𝑙(𝑠) β†’ 𝐴𝑙₂𝑂₃ (𝑠) + 2𝐹𝑒(𝐼)

Correct Answer: (a) Ferric oxide
Solution:

In the reaction 𝐹𝑒₂𝑂₃ (π‘“π‘’π‘Ÿπ‘Ÿπ‘–π‘ π‘œπ‘₯𝑖𝑑𝑒) + 2𝐴𝑙 (π΄π‘™π‘’π‘šπ‘–π‘›π‘–π‘’π‘š) β†’ 𝐴𝑙₂𝑂₃  (π΄π‘™π‘’π‘šπ‘–π‘›π‘–π‘’π‘š 𝑂π‘₯𝑖𝑑𝑒) + 2𝐹𝑒 (πΌπ‘Ÿπ‘œπ‘›)
The substance that is oxidized is Al and the substance that is reduced is Fe. when oxygen is added to an element, then this element is said to be oxidized. If oxygen is removed from any compound, then this compound is said to be reduced.

2. The coefficients a, b and c in the given balanced chemical equation are: [RRC Group D 11/10/2022 (Evening)]

aHN𝑂₃  (aq) +bCa(OHβ‚‚) (aq)β†’ Ca(N𝑂₃)β‚‚ + 𝑐𝐻₂O

Correct Answer: (c) 2, 1 and 2, respectively
Solution:

Balanced Chemical Equation: An equation where the number of atoms of each type in the reaction is the same on both reactants and product sides. Example: Fe (Iron) + Hβ‚‚O (Water) β†’ Fe₃Oβ‚„ (Ferrous - Ferric oxide) + Hβ‚‚ (Hydrogen) ; After balancing ; 3Fe + 4Hβ‚‚O β†’ Fe₃Oβ‚„ + 4Hβ‚‚ .

3. Which of the following is NOT a chemical weathering process? [RRB NTPC CBT - II (13/06/2022) Shift 2]

Correct Answer: (c) Thermal expansion
Solution:

Thermal expansion - The tendency of materials to expand or contract in response to changes in temperature. Chemical weathering - It changes the molecular structure of rocks and soil.
The processes of chemical weathering are solution, carbonation, hydration, oxidation and reduction. These processes act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and soil water and other acids.

4. Which of the following chemical reactions is a combination reaction? ( Here A, B, C and D represent any element/molecule). [RRB NTPC CBT - II (15/06/2022) Shift 2]

Correct Answer: (a) A+B→AB
Solution:

Combination reaction: Two or more compounds combine to form one compound. AB β†’ A + B - Decomposition reaction: A complex molecule breaks down to make simpler ones.
AB + C β†’ AC + B - Displacement reaction: One element takes place with another element in the compound. AB + CD β†’ AD + BC - Double Displacement Reaction: Ions get exchanged between two reactants which form a new compound.

5. A solution reacts with chalk powder to give a gas that turns lime water milky. The solution contains [RRB NTPC CBT - I (30/12/2020) Evening]

Correct Answer: (a) HCl
Solution:

In the chemical reaction between Calcium Carbonate (CaCO₃ ) and Hydrochloric acid (HCl), carbon dioxide (COβ‚‚) gas is formed. Chemical Reaction: CaCO₃  + 2HCl β†’ CaClβ‚‚ + Hβ‚‚O + COβ‚‚ ; HCL is primarily used as a bleaching agent in food, textile, metal and rubber industries.

6. The Rate constant of a reaction doubles with a______ rise in temperature. [RRB NTPC CBT - I (05/01/2021) Evening]

Correct Answer: (b) 10 degrees
Solution:

Rate Constant (K) - It is the proportionality constant in the equation that expresses the relationship between the rate of a chemical reaction and the concentrations of the reacting substances.
It is directly proportional to temperature. Rate = k [A]β‚˜ [B]β‚™ . Where, "Rate" is the rate of the reaction. "k" is the rate constant. "[A]" and "[B]" are the concentrations of the reactants A and B, respectively. "m" and "n" are the reaction orders with respect to A and B, respectively.

7. Which of the following methods can be used for separating a mixture of NaCl and NHβ‚„Cl? [RRB NTPC CBT - I (19/01/2021) Morning]

Correct Answer: (a) Sublimation
Solution:

Sublimation is the process of a solid changing directly into a gas without passing through a liquid state. Other methods of separating mixtures - Chromatography (Based on the different rates at which the components travel through a stationary phase).
Crystallisation (Based on the different solubilities of the components). Centrifugation (Based on the different densities of the components).

8. Which of the following in the air turns silver articles black (when exposed to air)? [RRB NTPC CBT - I (01/02/2021) Evening]

Correct Answer: (c) Sulphur
Solution:

Silver reacts with Sulphur compounds such as Hydrogen Sulphide (Hβ‚‚S) present in the air to get tarnished silver. 4Ag (polished silver) + 2Hβ‚‚S + Oβ‚‚ β†’ 2Agβ‚‚S (Tarnished silver) + 2Hβ‚‚O.
Silver (Ag, 47) - A soft, white, lustrous transition metal. It exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. Sulphur (S, 16) - It is a bright yellow, crystalline solid at room temperature.

9. What is oxidization? [RRB NTPC CBT - I (09/02/2021) Evening]

Correct Answer: (b) A substance gaining oxygen during a chemical reaction
Solution:

Oxidation - A chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance. Examples of oxidation - Rusting of Iron, the brown color on a cut apple. Reduction - Gain of hydrogen and loss of oxygen.

10. Which of the following is true regarding 𝐢𝑂₂ ? [RRB NTPC CBT - I (10/02/2021) Morning]

Correct Answer: (d) The solid form of 𝐢𝑂₂ is called dry ice.
Solution:

Dry ice is colourless, odourless in nature and used to preserve frozen food items. When carbon dioxide (COβ‚‚) reacts with water (Hβ‚‚O), it forms carbonic acid (Hβ‚‚CO₃).
Reaction Equation: COβ‚‚ + Hβ‚‚O β‡Œ Hβ‚‚CO₃ . COβ‚‚ is a linear molecule with a central carbon atom bonded to two oxygen atoms and forms a Covalent bond.