Railway Science (Chemistry-Chemical Properties)

Total Questions: 52

1. Study the given diagram carefully. Which option correctly explains the reason for the appearance of the blue black colour? [RRC Group D 17/08/2022 (Afternoon)]

Correct Answer: (c) Potato juice contains starch, which turns blue black with iodine
Solution:

Potatoes are a rich source of starch. Iodine (I) reacts with Starch (C₆H₁₀O₅)ₙ which produces a blue black color. Iodine is used in Photography, the Pharmaceutical industry, and water purifiers.

2. Consider the below statements and identify the correct answer. [RRC Group D 17/08/2022 (Afternoon)]

Statement-I: Anhydrous sodium carbonate is used in soda-acid fire extinguishers.
Statement-II: Anhydrous sodium carbonate is dissolved in water and recrystallized to get washing soda crystals containing 10 molecules of water of crystallization

Correct Answer: (b) Statement-II is true, and Statement-I is false.
Solution:

Soda-acid fire extinguisher comprises sodium bicarbonate and sulphuric acid. Anhydrous sodium carbonate (soda ash) is dissolved in water and recrystallized to get washing soda crystals containing 10 molecules of water of crystallization and Its chemical formula is 𝑁𝑎₂𝐶𝑂₃. 10𝐻₂𝑂.

3. Consider the below statements and identify the correct answer. [RRC Group D 29/08/2022 (Afternoon)]

Statement - I : Plaster of Paris has a very remarkable property of setting into hard mass on wetting with water.
Statement - II : Plaster of Paris is used in chemistry laboratories for sealing air gaps in apparatus where air tight arrangement is required.

Correct Answer: (c) Both the statements are true.
Solution:

Plaster of paris (P.O.P) is calcium sulfate hemihydrate. Chemical formula- CaSO₄ ·½H₂O. It is prepared by heating Gypsum at 373 K. It should be kept in a sealed container so that it cannot react with moisture present in air.
Uses - Fireproofing material, preparing mould, statues and artificial decorative items, case of bone fracturing, blackboard chalks, dentistry etc.

4. Substance X, which is used as an antacid, reacts with dilute hydrochloric acid to produce a gas Y, which is used in one type of fire-extinguisher. The substance X and gas Y, respectively, are: [RRC Group D 29/08/2022 (Evening)]

Correct Answer: (c) NaHC𝑂₃, C𝑂₂
Solution:

Sodium bicarbonate (NaHC𝑂₃ , baking soda) is used as an antacid because it neutralizes excess acid present in the stomach. When sodium carbonate reacts with hydrochloric acid then carbon dioxide gas is evolved. The reaction is NaHC𝑂₃ + HCl → NaCl + C𝑂₂ + 𝐻₂𝑂.
Sodium bicarbonate use - Relieve heartburn, sour stomach, or acid indigestion by neutralizing excess stomach acid.

5. Which among the following is NOT a use of sodium hydroxide? [RRC Group D 01/09/2022 (Morning)]

(i) Used in making soaps and detergents.
(ii) Used in the manufacture of paper.
(iii) Used for removing permanent hardness of water.

Correct Answer: (c) Only iii
Solution:

Uses of Sodium hydroxide - To manufacture soaps, rayon, paper, explosives, dyestuffs, and petroleum products, in processing cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, degreasing metals, and electrolytic extracting. Sodium hydroxide (formula NaOH), also known as lye and caustic soda.

6. At what temperature does gypsum get converted into Plaster of Paris? [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (c) 373 K
Solution:

7. Which of the following coloured precipitates is formed when lead (II) nitrate and potassium iodide are mixed together? [RRC Group D 14/09/2022 (Evening)]

Correct Answer: (a) Yellow
Solution:

It is a type of double displacement reaction. The lead and potassium exchange their anions to give lead iodide and potassium nitrate. Pb(NO₃)₂ (Lead nitrate) + 2KI (Potassium Iodide) → PbI₂ (Lead iodide) + 2KNO₃ (Potassium Nitrate). It will form a yellow precipitate of lead iodide.

8. White AgCl turns gray in presence of: [RRC Group D 15/09/2022 (Morning)]

Correct Answer: (c) sunlight
Solution:

White AgCl (silver chloride) turns grey in sunlight due to the decomposition of silver chloride into silver and chlorine by light. AgBr (Silver bromide) also behaves in the same way. Silver chloride has been used as an antidote for mercury poisoning. The reaction that takes place is:

9. When electrolysis of brine is done, a gas X is formed at the cathode, which gives a pop sound when a burning splitter is brought near it. The gas X is: [RRC Group D 15/09/2022 (Evening)]

Correct Answer: (d) H₂
Solution:

Electrolysis of brine, reactions occur at the electrodes: At cathode:- 2H₂O + 2e⁻ → H₂ + 2OH⁻ , At anode:- 2Cl⁻− → Cl₂ + 2e⁻ . A cathode is the metallic electrode through which current flows out in a polarized electrical device. Cathodes get their name from cations (positively charged ions) and anodes from anions (negatively charged ions). An anode is an electrode of a polarized electrical device through which conventional current enters the device.

10. When zinc granules react with dilute sulphuric acid, a colourless gas is produced which burns with a: [RRC Group D 16/09/2022 (Morning)]

Correct Answer: (d) pop sound
Solution:

Hydrogen gas is evolved mostly, when a metal reacts with an acid. When zinc reacts with dilute sulphuric acid, zinc sulphate, a salt, is formed with the release of hydrogen gas. The reaction involved is:- Zn(s) + H2SO₄(l)→ZnSO₄(s) + H₂(g). Its single displacement reaction.