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

Total Questions: 50

21. Which of the following reactions is commonly used in the hydrogenation of vegetable oils using a nickel on catalyst? [RRB JE 24/05/2019 (Evening)]

Correct Answer: (a) Addition reaction
Solution:

Addition reaction occurs when two or more reactants combine to form a product without the loss of any atoms present in the reactants. Example : 3Fe (Iron) + 2O₂ (Oxygen) Fe₃O₄ → (Iron Oxide).
Hydrogenation is a chemical process that occurs when molecular hydrogen (H₂) reacts with another unsaturated substance in the presence of a catalyst like Nickel (Ni), Palladium (Pa), or Platinum (Pt).

22. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following CORRECTLY represents the type of reaction involved? [RRB JE 25/05/2019 (Morning)]

Correct Answer: (d) Precipitation reaction
Solution:

Precipitation reaction: The reaction in which two compounds exchange ions to form two new compounds out of which one is an insoluble compound (called precipitate). Example: BaCl₂ + (NH₄)₂SO₄ → BaSO₄ + 2NH₄Cl.

23. Which of the following reactions is an example of an endothermic reaction? [RRB JE 25/05/2019 (Afternoon)]

Correct Answer: (b) Decomposition of ferrous sulphate
Solution:

An endothermic reaction is any chemical reaction that absorbs heat from its environment. Examples - Photosynthesis, dry ice, alkane cracking, ammonium chloride in water, and evaporating liquids.
An exothermic reaction is a chemical reaction that releases energy in the form of heat or light. Example - Burning of natural gas, dilution of sulphuric acid, and dissolution of sodium hydroxide in water.

24. When a decomposition reaction is carried out by heating, it is called- [RRB JE 25/05/2019 (Evening)]

Correct Answer: (a) Thermal decomposition
Solution:

Thermal decomposition - A chemical reaction that happens when a compound breaks down when heated. The reactants absorb lots of energy before breaking down into the products. Example - CuCO₃ (Copper Carbonate)(s) → CuO (Copper oxide)(s) + CO₂ (Carbon dioxide)(g).
Decomposition reaction - chemical reaction in which one reactant breaks down into two or more products. General format: AB → A + B. Electrolytic decomposition reaction - Activation energy for decomposition is provided in the form of electrical energy.
Photodecomposition reaction - Decomposition reaction in which the reactant absorbs energy from photons and breaks down into its parts. Example - Decomposition of ozone into dioxygen and an oxygen radical.

25. Mn𝑂₂ + 4HCI → Mn𝐶𝑙₂ +2𝐻₂0 + 𝐶𝑙₂ is an example of - [RRB JE 26/05/2019 (Morning)]

Correct Answer: (d) Redox reaction
Solution:

Redox reaction (oxidation-reduction reaction) - The reaction in which oxidation and reduction take place simultaneously, that is the loss of an electron from one reactant, and gain of electron to the other. In such reactions, one element gets reduced, and the other gets oxidized.

26. What happens when calcium is treated with water? [RRB JE 26/05/2019 (Afternoon)]

i) It does not react with water.
ii) It reacts violently with water.
iii) It reacts less violently with water.
iv) Bubbles of hydrogen gas formed stick to the surface of calcium.

Correct Answer: (d) (iii) and (iv)
Solution:

Chemical reaction - Ca (Calcium) + 2H₂O (water) → Ca(OH)₂ (Calcium hydroxide or slaked lime) + H₂ (Hydrogen). Calcium is a member of the alkaline-earth metals of Group II of the Modern periodic table. Group II elements react vigorously with water, but not as violently as the Group I (alkali metals) such as Sodium (Na) or potassium (K).

27. The reaction of sodium sulfate and barium chloride solution is an example of- [RRB JE 26/05/2019 (Evening)]

Correct Answer: (b) Double displacement reaction
Solution:

Double displacement reaction - Generally takes place in aqueous solutions in which the ions precipitate and there is an exchange of ions. Example: Na₂SO₄ + BaCl₂→ BaSO₄+ 2NaCl.
Single-displacement reaction - A chemical reaction in which one element replaces other elements in a compound. Example: Mg + 2HCl → MgCl₂ + H₂ . Endothermic process - Heat is absorbed by the system from the surrounding. Exothermic process - Heat is released by the system into the surrounding.

28. During a chemical reaction, atomic number ______. [RRB JE 27/05/2019 (Morning)]

Correct Answer: (a) Remains the same
Solution:

The atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. In a chemical reaction the atomic number is not changed because protons do not take part in the chemical reaction.
During a chemical reaction the bonds between the atoms are broken and atoms are rearranged and the number of electrons is changed. Atomic mass is also not changed in chemical reactions.

29. In the reaction MgO+ CO→Mg + C𝑂₂ the substance oxidized is- [RRB JE 27/05/2019 (Afternoon)]

Correct Answer: (d) Carbon monoxide
Solution:

Magnesium oxide (MgO) is reduced. Oxidation - The addition of oxygen/electronegative elements to a substance or removal of hydrogen/electropositive elements from a substance.
Reduction - Removal of oxygen/electronegative element from a substance or addition of hydrogen/electropositive element to a substance.

30. In blast furnace, iron oxide is reduced by- [RRB JE 27/05/2019 (Afternoon)]

Correct Answer: (b) Carbon monoxide
Solution:

The production of iron from its ore involves an oxidation-reduction reaction carried out in a blast furnace. Carbon monoxide is used to reduce iron because carbon is a more reactive element than iron.
Carbon reacts with oxygen to form carbon monoxide and then that carbon monoxide reacts with iron oxide to form elemental iron. 2C + O₂ → 2CO₂  , Fe₂O₃ (Iron Oxide) + 3CO → 2Fe + 3CO₂ .