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

Total Questions: 50

1. Which of the following is obtained as a result of complete combustion of hydrocarbons? [RRB Group D 20/09/2018 (Morning)]

Correct Answer: (a) CO₂ + H₂O
Solution:

Incomplete combustion (where there is not enough oxygen present) can lead to the formation of carbon or carbon monoxide.

2. _______ on mixing with water changes to gypsum. [RRB Group D 20/09/2018 (Afternoon)]

Correct Answer: (d) Calcium Sulphate Hemihydrate
Solution:

Calcium Sulphate Hemihydrate (CaSO₄ . 1/2H₂O)- It is the 1 2 chemical name of plaster of Paris. Gypsum is a common sulfate mineral composed of calcium sulfate dihydrate. Bicarbonate of Soda (NaHCO₃) - It is commonly known as baking soda. Calcium phosphate (Ca₃ (PO₄)₂) - It is used to treat calcium deficiencies.

3. The equation 2Cu + O₂ → 2CuO is an example of a __________ reaction. [RRB Group D 20/09/2018 (Evening)]

Correct Answer: (d) combination
Solution:

Combination Reaction- A reaction in which two or more substances combine to form a single new substance. Example: C + O₂ → CO₂ .

4. What is exchanged between the reactants during a double decomposition reaction? [RRB Group D 20/09/2018 (Evening)]

Correct Answer: (c) Ions
Solution:

Double displacement reaction - A reaction in which part of one reactant is replaced by part of another reactant. Examples - AgNO₃ + NaCl → AgCl + NaNO₃ . Ions - It is an atom or molecule which has lost or gained one or more electrons, and carries a net electric charge. Electron - Discovered by J.J. Thomson. The number of electrons in a neutral atom is equal to the number of protons.

5. Which of the following is a balanced chemical equation? [RRB Group D 22/09/2018 (Afternoon)]

Correct Answer: (a) 2Mg + O₂→ 2MgO
Solution:

Balanced chemical reaction: An equation that has an equal number of atoms of each element on both sides of the equation. The mass of the reactants is equal to the mass of the products.
Example: 2 P₂O₅(aq) + 6H₂O(l) → 4H₃PO₄(aq), 6 CO₂(g) + 6H₂O(l) → C₆H₁₂O₆ + 6O₂(g), HCl(aq) + NaOH(aq) → NaCl(s) + H₂O(l) etc.

6. When washing soda reacts with hydrochloric acid ________ gas is evolved. [RRB Group D 22/09/2018 (Evening)]

Correct Answer: (c) Carbon dioxide
Solution:

Uses (CO₂) - As a refrigerant, in fire extinguishers, for inflating life rafts and life jackets, blasting coal, foaming rubber and plastics, promoting the growth of plants in greenhouses, immobilizing animals before slaughter, and in carbonated beverages. Washing soda (Na₂CO₃). Reaction : 2HCl (aq) + Na₂CO₃ (aq) ⟶ 2NaCl (aq) + CO₂ (g) +H₂O (l). It is a double displacement type of reaction.

7. When copper oxide is heated with hydrogen, copper metal and water are formed. What happens to the hydrogen in this reaction? [RRB Group D 23/09/2018 (Afternoon)]

Correct Answer: (c) Oxidation
Solution:

Oxidation : It is the loss of electrons during a reaction by a molecule, atom or ion. Oxidizing agent (O₂ , S, Cl₂ , Br₂ , H₂O₂). Reduction - It is a reaction when there is a gain of electrons and a loss of Oxygen.

8. Silver chloride is stored in a dark bottle: [RRB Group D 23/09/2018 (Evening)]

Correct Answer: (c) to avoid reaction with sunlight
Solution:

When exposed to sunlight, silver chloride (AgCl) decomposes into silver (Ag) and chlorine gas, which are both toxic. Compounds like Silver chloride are light sensitive and they may react to light very fast and lose their properties.

9. Dissolving an acid or an alkali in water is known as? [RRB Group D 24/09/2018 (Afternoon)]

Correct Answer: (d) exothermic reaction
Solution:

exothermic reaction : It releases energy by light or heat to its surroundings. Dissolving acids and alkalis typically releases heat. Endothermic reaction: This type of reaction absorbs heat from the surroundings. Examples: Dissolving salt in water, Photosynthesis, Water evaporation.

10. A thermal reaction is a reaction in which : [RRB Group D 24/09/2018 (Afternoon)]

Correct Answer: (b) Heat is released
Solution:

A thermal reaction is a kind of chemical reaction that happens as a consequence of an increase in temperature. Exothermic reactions: A chemical reaction that releases energy in the form of heat or light. Endothermic Reactions: A chemical reaction in which the heat is absorbed.