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

Total Questions: 50

31. On heating ethanol with concentrated H₂SO₄ , at 443 K gives- [RRB JE 27/05/2019 (Evening)]

Correct Answer: (a) Ethene
Solution:

32. The white powder formed when magnesium ribbon burns is- [RRB JE 28/05/2019 (Morning)]

Correct Answer: (b) Magnesium oxide
Solution:

2Mg (Magnesium) + O₂ (Oxygen) → 2MgO (Magnesium oxide) + energy. A bright white light is produced when the ribbon is burnt and powdery ash i.e. MgO is formed. The reaction is a highly exothermic reaction (a lot of heat is produced). Magnesium Oxide is used as an antacid to relieve heartburn, sour stomach, or acid indigestion.

33. PbO₂ + 4HCl → PbCl₂ + 2H₂O + Cl₂ the substance undergoing oxidation is __ [RRB JE 29/05/2019 (Morning)]

Correct Answer: (c) Hydrochloric acid
Solution:

Oxidation - The loss of electrons during a reaction by a molecule, atom or ion. It occurs when the oxidation state of a molecule, atom or ion is increased. Reduction - The transfer of electrons between species in a chemical reaction where there is a process of gaining electrons or a decrease in the oxidation state by an element.

34. Identify the products in the equation Na₂CO₃ + 2HCl → [RRB JE 29/05/2019 (Afternoon)]

Correct Answer: (d) 2NaCl +CO₂ + H₂O
Solution:

When sodium carbonate (Na₂CO₃) reacts with hydrochloric acid (HCl) two moles of Sodium chloride and carbonic acid are formed. The carbonic acid further dissolves to form water (H₂O) and Carbon dioxide (CO₂).

35. A dilute ferrous sulfate solution was gradually added to the beaker containing acidified potassium permanganate solution. The light purple color of the solution fades and finally disappears. Which of the following is the CORRECT explanation for the observation? [RRB JE 29/05/2019 (Evening)]

Correct Answer: (a) Potassium permanganate is an oxidizing agent, it oxidizes ferrous sulfate
Solution:

Potassium permanganate (KMnO₄) in presence of dilute H₂SO₄ acts as a strong oxidizing agent and oxidized ferrous sulfate (FeSO₄) to ferric sulfate. Hence, the purple color fades and finally disappears.

36. Which of the following salts is used in the preparation of sodium hydroxide, baking soda, washing soda? [RRB JE 29/05/2019 (Evening)]

Correct Answer: (a) Sodium chloride
Solution:

Sodium chloride (NaCl) is used to treat or prevent sodium loss caused by dehydration, excessive sweating, or other causes. It is used to prepare sodium hydroxide (2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ ), baking soda (NaCl + NH₃ + H2O + CO₂ → NaHCO₃ + NH₄Cl) and washing soda ( 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O). Compounds and Name : NH₃ (Ammonia), H₂O (Dihydrogen oxide), Na₂CO₃ (Washing soda), NaHCO₃ (Baking soda), NH₄Cl (Ammonium Chloride).

37. What type of reaction is electrolysis of water? [RRB JE 30/05/2019 (Evening)]

Correct Answer: (c) Decomposition reaction
Solution:

Decomposition reaction is a chemical process in which a single reactant breaks up into multiple products. Electrolysis of water is a good example of an electrolytic decomposition reaction.
2H₂O (water) + O₂ (Oxygen) → 2H₂ (Hydrogen)+ 2O₂ (Oxygen). Combination reactions: Reactions in which two or more reactants combine to form one product. Example - Mg (Magnesium) + O₂ (Oxygen) → 2MgO (Magnesium Oxide).

38. When copper oxide is heated with hydrogen, copper metal and water are formed. What happens to the copper oxide in this reaction? [RRB JE 31/05/2019 (Morning)]

Correct Answer: (a) Reduced
Solution:

Reaction - CuO (copper oxide) + H₂ (hydrogen) → Cu (copper) + H₂O (water). In this reaction, the oxidation state of Cu in copper oxide is +2 and that of H in hydrogen is 0 at reactant side, but oxidation state of Cu in copper is 0 and that of H in water is +1.
So, that H₂ is getting oxidized since its oxidation number is increasing and CuO is getting reduced since its oxidation number is decreasing.

39. The reaction between sodium hydroxide with zinc gives the product- [RRB JE 31/05/2019 (Morning)]

Correct Answer: (c) Sodium zincate
Solution:

The reaction is : Zn (zinc) + 2NaOH (sodium hydroxide) 2Na₂ZnO₂ → (Sodium zincate) + H₂ (hydrogen gas). It is an example of a single displacement reaction. It occurs when another element in a compound is replaced by an element. It is represented by (A + BC → AB + C).

40. Reactions involving loss of hydrogen is known as- [RRB JE 01/06/2019 (Afternoon)]

Correct Answer: (d) Oxidation reaction
Solution:

Oxidation reaction - Oxidation is the gain of oxygen. Example - 2Mg + O₂→ 2MgO.
Reduction Reaction: A reaction in which either the addition of Hydrogen takes place or the removal of oxygen takes place. Example is: N₂ + 3 H₂ → 2NH3
Combination reaction: Reactions in which two or more reactants combine to form one product. Examples: 2Mg+O₂→2MgO.
Decomposition reaction: A chemical reaction in which one reactant breaks down into two or more products. Example: 2HgO(s) → 2Hg(l) + O₂(g).