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

Total Questions: 19

11. When lead metal reacts with a solution of copper chloride, then: [RRB Group D 15/11/2018 (Afternoon)]

Correct Answer: (d) Lead chloride is formed
Solution:

When a strip of lead metal is placed in a solution of copper chloride then lead chloride and copper are formed. The green colour of copper chloride fades and the solution becomes colourless.

12. The given reaction is an example of _______. [RRB Group D 16/11/2018 (Evening)]

BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl

Correct Answer: (d) double displacement reaction
Solution:

double displacement reaction: In this, the cations (positively charged ions) of two ionic compounds exchange places, thereby forming two new ionic compounds. Displacement reaction: This occurs when a more reactive element in a compound replaces a less reactive element during a chemical reaction.

13. When crystals are heated, water of crystallisation is lost and the substance turns into a/an____ form. [RRB Group D 27/11/2018 (Morning)]

Correct Answer: (d) anhydrous
Solution:

Anhydrous - The salts which have lost their water of crystallization Example - Copper sulfate (CuSO₄) crystals are blue in colour. When copper sulfate crystals are heated strongly,they lose water of crystallization and form anhydrous copper sulfate which is white in color.
Crystallization is a process by which a pure soluble substance separates out in the form of crystals from its hot and saturated solution on cooling. Example - The crystallization of water forms ice cubes and snow.

14. _______ is also called quick lime. [RRB Group D 3/12/2018 (Afternoon)]

Correct Answer: (d) Calcium oxide
Solution:

Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat. Example : CaO(s) (Quick lime) + H₂O(l) → Ca(OH)₂ (aq) (Slaked lime) + Heat .
In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction.

15. Select the correct alternative that represents the answers for statements A and B respectively.: [RRB Group D 07/12/2018 (Afternoon)]

A. What is the fixed number of water  molecules present in a formula unit of salt ?
B. What is the number of water molecules in CuSO₄.5H₂O ?

Correct Answer: (b) Crystallization water, five
Solution:

Five water molecules are present in one formula unit of copper sulphate. The chemical formula for hydrated copper sulphate is CuSO₄.5H₂O.

16. What are the products formed as a result of thermal decomposition of lead nitrate ? [RRB Group D 11/12/2018 (Afternoon)]

Correct Answer: (a) Lead oxide + oxygen + nitrogen dioxide
Solution:

17. A mixture of ethyne and ________ is used for welding. [RRB Group D 12/12/2018 (Evening)]

Correct Answer: (b) oxygen
Solution:

18. The main cause of rancidity in foods is the_________ of fats and oils. [RRB ALP Tier - I (09/08/2018) Afternoon]

Correct Answer: (a) oxidation
Solution:

Rancidity - Condition in which incomplete oxidation or hydrolysis of fats and oils takes place that spoils the food. It occurs when food is exposed to light, air, moisture or to any bacterial action.
Oxidation and Reduction reactions - The chemical reactions which involve the transfer of electrons from one chemical substance to another. Hydrolysis is a chemical reaction in which a compound is broken down by reacting with water.
Clarification - It usually applies to the removal of small concentrations of solid particles from fluids.

19. In the reaction H₂O₂ + Cl₂ → 2HCl + O₂ , H₂O₂ acts as:( chemical reaction) [RRB ALP Tier - I (10/08/2018) Afternoon]

Correct Answer: (d) a reducing agent
Solution:

It is a substance which loses electrons and gets oxidized which leads to the increase in oxidation state. It reduces the other substance. Example - H₂O₂ (Hydrogen Peroxide) + Cl₂ (Chlorine) → 2HCl (Hydrochloric Acid) + O₂ (Oxygen).
An oxidizing agent is a substance which gains electrons and gets reduced which leads to the decrease in oxidation state. It oxidizes the other substance. Example - Fe₂O₃ {Iron (III) Oxide} + 3CO (Carbon monoxide) 2Fe (Iron) + 3CO₂ → (Carbon dioxide).