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

Total Questions: 50

31. Which of the following observations helps us determine whether a chemical reaction has occurred or not ? [RRB Group D 09/10/2018 (Afternoon)]

Correct Answer: (d) All these options
Solution:

When two or more molecules combine to produce a new product, it is called a chemical reaction. The characteristics of a chemical reaction are: Evolution of gas, Formation of a precipitate, Change in color, Change in temperature, Change in state etc.

32. While white washing, Ca(OH)₂ reacts slowly with the ________ in the air to form a thin layer of CaCO₃ on the walls. [RRB Group D 09/10/2018 (Evening)]

Correct Answer: (c) CO₂
Solution:

Slaked lime (Ca(OH)₂ is used for white washing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. Reaction involved : Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

33. _______ reacts more with water to form slaked lime. [RRB Group D 10/10/2018 (Morning)]

Correct Answer: (c) CaO
Solution:

When quicklime (CaO) reacts with water (H₂O), it undergoes a highly exothermic reaction to form calcium hydroxide (Ca(OH)₂), also known as slaked lime. The reaction involved is: CaO + H₂O ⟶Ca(OH)₂ + Heat.
Calcium Oxide: It appears as an odorless, white or gray-white solid in the form of hard lumps. It is a member of the class of calcium oxides of calcium and oxygen in a 1:1 ratio. Used in insecticides and fertilizers.

34. In the presence of sunlight _________ is added to hydrocarbons in a more rapid reaction. [RRB Group D 10/10/2018 (Evening)]

Correct Answer: (d) Cl₂
Solution:

In the presence of sunlight, chlorine reacts with saturated hydrocarbons and the process is called halogenation of hydrocarbons. In this reaction, the hydrogen atoms in the hydrocarbon are substituted by the chlorine atoms.

35. Which one of the following is exothermic? [RRB Group D 10/10/2018 (Evening)]

Correct Answer: (c) Dissolving sulfuric acid in water
Solution:

Reactions in which heat is released along with the formation of products are called exothermic chemical reactions. Other examples of exothermic reactions are - Burning of natural gas , The decomposition of vegetable matter into compost.

36. ________Corrosion is a serious problem. [RRB Group D 10/10/2018 (Evening)]

Correct Answer: (d) Fe
Solution:

Iron corrosion refers to the chemical reaction between iron and its environment, typically oxygen and moisture, leading to the formation of iron oxide (rust) on the surface of iron. Chemical formula (Rusting of the iron) - 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ .

37. In dehydration of ethanol by heating ethanol at 443K with more concentrated H₂SO₄, we get: [RRB Group D 10/10/2018 (Evening)]

Correct Answer: (d) ethene
Solution:

Ethylene (IUPAC name: ethene) is a hydrocarbon. It appears as a colorless gas with a sweet odor and taste. Molecular Formula: C₂H₄.

38. Which of the following options is a chemical change? [RRB Group D 12/10/2018 (Morning)]

Correct Answer: (a) converting milk into curd
Solution:

This process involves the fermentation of milk by bacteria, which breaks down lactose (milk sugar) into lactic acid. This acidification curdles milk proteins, forming curd, a new substance with different properties.

39. Magnesium ribbon burns with a dazzling ________ flame. [RRB Group D 12/10/2018 (Evening)]

Correct Answer: (b) white
Solution:

Magnesium ribbon burns with a dazzling white flame and changes into a white powder. This powder is magnesium oxide. Magnesium + oxygen → Magnesium oxide

40. _______ reaction requires energy to split the reactants. [RRB Group D 15/10/2018 (Morning)]

Correct Answer: (b) Decomposition
Solution:

Decomposition - A single reactant breaks down to give simpler products.The decomposition of carbonic acid in soft drinks, which can be represented by H₂CO₃ → H₂O + CO₂ . When heated, calcium carbonate decomposes into calcium oxide and carbon dioxide. Example, CaCO₃ → CO₂ .