CHEMISTRY (Part-I) (Railway)

Total Questions: 50

31. Which of the following causes damage to bridges, iron railings and all objects made of metals? [RRB ALP & Technician Exam,14.08.2018 Shift-1]

(1) Reduction
(2) Rancidity
(3) Acidity
(4) Corrosion

Correct Answer: (4) Corrosion

Solution:Corrosion is the wearing away of metals due to chemical reactions, mainly oxidation. In this process, metals lose their metallic properties. This causes a lot of damage to car bodies, ships, bridges, iron railings and to all objects made of iron. Corrosion that occurs on materials made of iron is 'rusting'.

32. Which, is the first metallic element in the Modern Periodic Table? [RRB ALP & Technician Exam,14.08.2018 Shift-I]

(1) LI
(2) Na
(3) He
(4) H₂

Correct Answer: (1) LI

Solution:The first two elements of the modern periodic table are Hydrogen and Helium, both are gases. Lithium is the first metallic element. It is placed third in the periodic table. after Hydrogen and Helium. It is placed in Group I along with other alkali metals such as Sodium (Na), Potassium (K), Rubidium (Rb) and Cesium (Cs).

33. Which of the following compounds has a double bond? [RRB ALP & Technician Exam,14.08.2018 Shift-I]

(1) Acetylene
(2) Ethene
(3) Ethane
(4) Methane

Correct Answer: (2) Ethene

Solution:Ethylene (also known as ethene) is a hydrocarbon which has the formula C₂H₄ or H2C = CH2. It contains two carbon atoms that are double bonded to each other, with each of these atoms also bonded to two Hydrogen atoms. This forms a total of three bonds to each carbon atom.

34. Name the reddish brown gas evolved when Lead Nitrate is heated strongly. [RRB ALP & Technician Exam. 14.08.2018 Shift-I]

(1) Nitric Oxide
(2) Nitrogen dioxide
(3) Di Nitrogen Oxide
(4) Nitrogen pentoxide

Correct Answer: (2) Nitrogen dioxide

Solution:When solid lead nitrate is heated strongly, it turns yellow due to formation of lead oxide and a reddish brown gas is evolved which is nitrogen dioxide. When the evolved gas is passed over wooden glowing splinters, it rekindles. This shows the presence of oxygen. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

35. Which of the following gases is liberated when Sodium Hydrogen Carbonate is heated? [RRB ALP & Technician Exam,14.08.2018 Shift-III]

(1) Hydrogen
(2) Carbon Monoxide
(3) Carbon Dioxide
(4) Oxygen

Correct Answer: (3) Carbon Dioxide

Solution:

On heating sodium hydrogen carbonate (NaHCO₃), it decomposes to form sodium carbonate (Na₂CO₃), water (H₂O) and carbon dioxide (CO₂). The chemical reaction is: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

36. How are elements arranged in the Modern Periodic Table? [RRB ALP & Technician Exam,14.08.2018 Shift-III]

(1) In the increasing order of their Atomic Number
(2) In the increasing order of their Mass Number
(3) In the increasing order of their Molecular Mass
(4) In the increasing order of their Atomic Mass

Correct Answer: (1) In the increasing order of their Atomic Number

Solution:The modern Periodic law can be stated as: "the physical and chemical properties of the elements are periodic functions of their atomic numbers". Atomic number is equal to the number of electrons or protons in a neutral atom. The elements are arranged based on their increasing atomic number. There are 7 periods and 18 groups in the table.

37. Which of the following indicators CANNOT be used for distinguishing between acidic and neutral solutions? [RRB ALP & Technician Exam, 14.08.2018 Shift-III]

(1) Methyl orange
(2) Phenolphthalein
(3) Eosin
(4) Universal indicator

Correct Answer: (2) Phenolphthalein

Solution:Phenolphthalein is often used as an indicator in acid-base titrations. For this application, it turns colourless in acidic solutions and magenta in basic solutions. Below a pH of 8.2 Phenolpthalein is colourless. Above this pH it turns pink indicating basic nature. Hence, this indicator cannot be used for distinguishing between acidic and neutral solutions.

38. ________is amphoteric in nature. [RRB ALP & Technician Exam,14.08.2018 Shift-III]

(1) SO₂
(2) N₂O
(3) CaO
(4) ZnO

Correct Answer: (4) ZnO

Solution:An amphoteric compound is a molecule or ion that can react both as an acid and as a base. Many metals (such as copper, zinc, tin, lead, aluminum, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation states of the oxide. ZnO reacts with hydrochloric acid, forming zinc chloride and water. With sodium hydroxide, it forms sodium zincate and water.

39. Which of the following metals CANNOT be easily cut with a knife? [RRB ALP & Technician Exam,14.08.2018 Shift-III]

(1) Aluminium
(2) Sodium
(3) Potassium
(4) Lithium

Correct Answer: (1) Aluminium

Solution:Lithium, sodium and potassium are all soft metals that are easily cut with a scalpel or knife. The freshly cut surface is a shiny, silver colour, but this tarnishes quickly to a dull grey as the metal reacts with oxygen and water in the air.

40. Which of the following salts is acidic in nature? [RB ALP & Technician Exam. 17.08.2018 Shift-I]

(1) Sodium Carbonate
(2) Sodium Acetate
(3) Ammonium Phosphate
(4) Magnesium Sulphate

Correct Answer: (4) Magnesium Sulphate

Solution:Aqueous solution of magnesium sulphate is slightly acidic. MgSO₄ is a salt formed by a weak base and a strong acid (both dibasic), so there is a two-step hydrolysis of magnesium cation.

First and primary step is the formation of a basic salt:
2MgSO₄ + 2 H₂O ⇌ Mg(OH)₂ SO₄ + H₂SO₄
2 Mg²⁺ + 2 SO₄²⁻ + 2 H₂O ⇌ 2 MgOH⁺ + SO₄²⁻ + 2 H⁺ + SO₄²⁻

Mg²⁺ + H₂O ⇌ MgOH⁺ + H⁺

In the second step:
(MgOH)₂SO₄ + 2 H₂O ⇌ 2 Mg(OH)₂ + H₂SO₄
2 MgOH⁺ + SO₄²⁻ + 2 H₂O ⇌2 Mg(OH)₂ + 2 H⁺ + SO₄²⁻
MgOH⁺ + H₂O ⇌ Mg(OH)₂ + H⁺

As a result of the hydrolysis reaction, some excess amount of hydronium cations appears, therefore, the medium is acidic.

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