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

Total Questions: 39

31. Which type of reaction occurs when carbon burns in oxygen to give carbon dioxide? [RRB ALP Tier - I (21/08/2018) Evening]

Correct Answer: (d) Combustion reaction
Solution:

Combustion reaction - A reaction in which a carbon compound burns in oxygen to produce carbon dioxide along with release of a large amount of heat and light. Equation - CH₄ (Methane) + 2O₂ (Oxygen) CO₂ → (Carbon Dioxide) + 2H₂O (Water) + energy.
Example - Burning of Wax candle, Combustion of petrol in a car's engine, Burning of natural gas in a bunsen burner, An explosion of hydrogen in air, Fireworks etc.

32. Which of the following is NOT true for the reaction of Calcium with water? [RRB ALP Tier - I (29/08/2018) Afternoon]

Correct Answer: (b) The reaction is less violent
Solution:

Quick lime {Calcium oxide (CaO)} combines with water to form slaked lime or Calcium Hydroxide {Ca (OH)₂}. CaO (s) + H₂O (l) →Ca(OH)₂ (aq) .The process releases a lot of heat and it is a kind of exothermic reaction (The release of energy in the form of heat or light in chemical reactions).

33. Which of the following is NOT a double displacement reaction? [RRB ALP Tier - I (29/08/2018) Afternoon]

Correct Answer: (b) Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃
Solution:

Mg₃N₂ (Magnesium Nitride) + 6H₂O (Water) 3Mg(OH) → 2 (Magnesium hydroxide) + 2NH₃ (Ammonia). Double displacement reaction - A chemical reaction where positive ions (cation) and the negative ions (anion) of two compounds react and change places to form two new products; Example - CuSO₄ (copper sulphate)+ H₂S (Hydrogen sulfide) → CuS (Copper sulfide) + H₂SO₄ (Sulfuric acid).

34. Fill in the blank with the most appropriate option. [RRB ALP Tier - I (30/08/2018) Afternoon]

Quicklime reacts with water to form ___ .

Correct Answer: (a) slaked lime
Solution:

When Calcium oxide (solid) is mixed with water it forms Calcium Hydroxide. The above reaction can be written as CaO + H₂O → Ca(OH)₂ . Limestone {CaCO₃/Calcium Carbonate}, Chloride of Lime {Ca(OCl)₂ /Calcium Hypochlorite}, Chalk Powder {composed of calcium carbonate (CaCO₃)}.

35. Which of the following is a chemical reaction? [RRB ALP Tier - I (30/08/2018) Afternoon]

Correct Answer: (d) Butter turning rancid
Solution:

Chemical Reaction - One or more substances, known as reactants, undergo a transformation to produce new substances, known as products. During a chemical reaction, the bonds between atoms are broken and reformed, resulting in a rearrangement of atoms to form different compounds. Examples of chemical reactions in day-to-day life - Combustion, Digestion, Baking, Rusting, Photosynthesis, Fermentation, Tarnishing (darkening of silver or copper objects), etc.

36. Which gas is released when bleaching powder is added to water? [RRB ALP Tier - I (30/08/2018) Evening]

Correct Answer: (b) Chlorine
Solution:

Bleaching powder on reaction with water produces calcium hydroxide and chlorine gas. CaOCl₂+H₂O → Ca(OH)₂+Cl₂ . Chlorine (Cl) is the second-lightest of the halogens, it appears between fluorine and bromine in the periodic table.
Atomic number - 17, Discovered - 1774 by Carl Wilhelm Scheele. Sodium chloride (NaCl) is the most common compound of chlorine whereas the simplest is hydrogen chloride (HCl). Hydrogen (H), Atomic number - 1, discovered - 1766 by Henry Cavendish. Bleaching powder - Chemical formula - CaOCl₂ .

37. When iron is exposed to moist air, a reddish brown coating of hydrated Iron (III) Oxide (Fe₂O₃) is deposited on its surface. This reddish brown coating is called: [RRB ALP Tier - I (31/08/2018) Afternoon]

Correct Answer: (d) rust
Solution:

It is an example of corrosion. Corrosion - The process by which a metal reacts with moisture, air and other substances. Chemical formula of rust - Fe₂O₃ .nH₂O. Alloy - Metallic substance composed of two or more elements, as either a compound or a solution. Example - Nichrome, Steel, Brass etc.

38. An unbalanced chemical equation is called a: [RRB ALP Tier - I (31/08/2018) Afternoon]

Correct Answer: (a) skeletal chemical equation
Solution:

Unbalanced Chemical equation - The total number of atoms of each element on the reactant side is not equal to the total number of atoms of each element in the product side. Example - Mg (s) +O₂ (g) → MgO (s) (Skeletal equation). Balanced Chemical equation - The total number of atoms of each element on the reactant side is equal to the total number of atoms of each element in the product side. Example - 2 Fe₂O₃(s) + 3C(s) → 4 Fe(s) + 3CO₂(g).

39. Which of the following statements is/are true or false? (chemical reaction) [RRB ALP Tier - I (31/08/2018) Evening]

Statements:
A) H₂S burns in air to give H₂O and SO₂
B) The decomposition of Ferrous Sulphate into Fe₂O₃ , SO₂ and SO₃ occurs in the presence of heat.

Correct Answer: (d) Statements A and B both are true
Solution:

Hydrogen sulfide is slightly heavier than air; a mixture of H₂S and air is explosive. Hydrogen sulfide and oxygen burn with a blue flame to form sulfur dioxide (SO₂) and water.
2H₂S(g) + 3O₂ (g) → 2H₂O(l) + 2SO₂(g). Decomposition of ferrous sulfate is an endothermic reaction as it involves absorption of heat to form ferric oxide (Fe₂O₃), sulphur dioxide (SO₂) and sulphur trioxide (SO₃). 2FeSO₄(s) → Fe₂O₃ (s) + SO₂(g) + SO₃(g).