Engineering Chemistry (DI01000071) - Winter 2024 Solution

Question 1 [14 marks]

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Fill in the blanks using appropriate choice from the given options:

Answer:

Mnemonic: “Chemical Copper Creates Beautiful Properties” (for remembering key concepts)

Question 2(A) [6 marks]

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Question 2(A)(1) [3 marks]

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List the three importance of pH in various fields.

Answer:

Mnemonic: “Medical Agriculture Industry” (MAI)

Question 2(A)(2) [3 marks]

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Define: Buffer solutions, Half-cell, Faraday’s first law of electrolysis.

Answer:

• Buffer solutions: Solutions that resist changes in pH when small amounts of acid or base are added
• Half-cell: Single electrode immersed in its ionic solution, represents oxidation or reduction reaction
• Faraday’s first law: Amount of substance deposited/liberated at electrode is directly proportional to quantity of electricity passed

Mnemonic: “Buffers Help Faraday” (BHF)

Question 2(A)(3) [3 marks]

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State the factors affecting the rate of corrosion.

Answer:

Mnemonic: “Pure Temperature Humidity” (PTH)

Question 2(B) [8 marks]

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Question 2(B)(1) [4 marks]

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Compare between orbits and orbitals (four points each).

Answer:

Diagram:

Mnemonic: “Definite Shape Energy Location” (DSEL)

Question 2(B)(2) [4 marks]

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Classify fuels on the basis of its sources and physical states with one example of each.

Answer:

Table:

Mnemonic: “Natural Artificial, Solid Liquid Gas” (NASLG)

Question 2(B)(3) [4 marks]

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Explain bio-diesel with four important points.

Answer:

• Source: Made from vegetable oils, animal fats, or waste cooking oil
• Process: Produced by transesterification reaction with methanol/ethanol
• Properties: Biodegradable, non-toxic, renewable fuel source
• Applications: Used in diesel engines, reduces emissions by 75%

Chemical Reaction:

Vegetable Oil + Methanol → Bio-diesel + Glycerol

Mnemonic: “Source Process Properties Applications” (SPPA)

Question 3(A) [6 marks]

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Question 3(A)(1) [3 marks]

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Explain solute, solvent and solution with the help of example.

Answer:

Example: Sugar + Water = Sugar solution

• Sugar = Solute, Water = Solvent, Sugar water = Solution

Mnemonic: “Solute Solvent Solution” (SSS)

Question 3(A)(2) [3 marks]

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Explain the formation of Electrovalent bond in NaCl.

Answer:

Process:

• Step 1: Na loses 1 electron → Na⁺ (cation)
• Step 2: Cl gains 1 electron → Cl⁻ (anion)
• Step 3: Electrostatic attraction between Na⁺ and Cl⁻

Diagram:

Mnemonic: “Sodium Loses, Chlorine Gains, Attraction Forms” (SLCGAF)

Question 3(A)(3) [3 marks]

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Explain Octane number for gasoline.

Answer:

Applications: High octane fuel prevents engine knocking, improves performance

Mnemonic: “Octane Opposes Knocking” (OOK)

Question 3(B) [8 marks]

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Question 3(B)(1) [4 marks]

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Explain electrorefining of impure Cu with chemical equations and a labeled diagram.

Answer:

Process:

• Anode: Impure copper dissolves
• Cathode: Pure copper deposits
• Electrolyte: CuSO₄ solution

Chemical Equations:

• At Anode: Cu → Cu²⁺ + 2e⁻
• At Cathode: Cu²⁺ + 2e⁻ → Cu

Diagram:

Mnemonic: “Anode Dissolves, Cathode Deposits” (ADCD)

Question 3(B)(2) [4 marks]

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Explain preparation of ethene with chemical equation. Also write its two properties and two uses.

Answer:

Preparation: C₂H₅OH → C₂H₄ + H₂O (Dehydration of ethanol)

Properties:

• Physical: Colorless gas, sweet smell
• Chemical: Unsaturated, undergoes addition reactions

Uses:

• Industrial: Manufacturing polyethylene
• Agricultural: Plant hormone for fruit ripening

Mnemonic: “Preparation Properties Uses” (PPU)

Question 3(B)(3) [4 marks]

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Explain preparation of Buna-S rubber with chemical equation. Also write its two properties and two uses.

Answer:

Preparation: Butadiene + Styrene → Buna-S rubber (Copolymerization)

Chemical Equation:

nC₄H₆ + nC₈H₈ → [-C₄H₆-C₈H₈-]ₙ

Properties:

• Mechanical: Good abrasion resistance
• Chemical: Oil and fuel resistant

Uses:

• Automotive: Tire manufacturing
• Industrial: Conveyor belts, hoses

Mnemonic: “Butadiene Styrene Makes Strong Rubber” (BSMSR)

Question 4(A) [6 marks]

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Question 4(A)(1) [3 marks]

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Explain metal clading for the prevention of corrosion of metals.

Answer:

Mechanism: Protective layer prevents oxygen/moisture contact with base metal

Mnemonic: “Coating Protects Metal” (CPM)

Question 4(A)(2) [3 marks]

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Explain waterline corrosion with chemical equations and labeled diagram.

Answer:

Process: Differential aeration causes corrosion at water-air interface

Chemical Equations:

• Anode: Fe → Fe²⁺ + 2e⁻
• Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O

Diagram:

Mnemonic: “Water Air Interface Corrodes” (WAIC)

Question 4(A)(3) [3 marks]

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Explain the working principle of solar cells.

Answer:

Process: Light → Electron excitation → Current flow → Electrical energy

Mnemonic: “Photo Voltaic Junction Creates Current” (PVJCC)

Question 4(B) [8 marks]

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Question 4(B)(1) [4 marks]

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Demonstrate the function of boundary lubrication with diagram.

Answer:

Function: Thin molecular layer adheres to metal surfaces, prevents direct contact

Mechanism:

• Formation: Lubricant molecules orient on metal surface
• Protection: Reduces friction and wear between surfaces
• Load bearing: Supports load when fluid film breaks down

Diagram:

Mnemonic: “Boundary Barriers Prevent Metal Contact” (BBPMC)

Question 4(B)(2) [4 marks]

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Explain how viscosity is measured through redwood viscometer with labelled diagram.

Answer:

Principle: Time taken for fixed volume of oil to flow through standard orifice

Procedure:

• Setup: Fill oil chamber, heat to required temperature
• Measurement: Record time for 50ml oil flow
• Calculation: Viscosity = Time × Constant

Diagram:

Mnemonic: “Redwood Records Time” (RRT)

Question 4(B)(3) [4 marks]

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Define: Semiconductor, Insulating material, Elastomer, Addition polymerization.

Answer:

Examples: Si (semiconductor), Rubber (insulator), Rubber (elastomer), Polyethylene (addition)

Mnemonic: “Semi Insulating Elastic Addition” (SIEA)

Question 5(A) [6 marks]

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Question 5(A)(1) [3 marks]

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Solve: Calculate the pH and pOH of 0.004 M HCl aqueous solution. (log 4 = 0.6021)

Answer:

Given: [HCl] = 0.004 M = 4 × 10⁻³ M

Solution:

• HCl is strong acid, completely ionizes
• [H⁺] = [HCl] = 4 × 10⁻³ M
• pH = -log[H⁺] = -log(4 × 10⁻³)
• pH = -log 4 - log 10⁻³ = -0.6021 + 3 = 2.398
• pOH = 14 - pH = 14 - 2.398 = 11.602

Answer: pH = 2.40, pOH = 11.60

Mnemonic: “Strong Acid, Simple Calculation” (SASC)

Question 5(A)(2) [3 marks]

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Describe extrinsic semiconductors and it types with examples.

Answer:

Properties:

• n-type: Extra electrons increase conductivity
• p-type: Electron deficiency creates positive holes

Mnemonic: “n-negative electrons, p-positive holes” (nnep)

Question 5(A)(3) [3 marks]

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Distinguish between thermoplastic polymers and thermosetting polymer (Four points of each)

Answer:

Mnemonic: “Thermo-plastic = Reversible, Thermo-setting = Permanent” (TPRTSP)

Question 5(B) [8 marks]

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Question 5(B)(1) [4 marks]

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Describe hydrogen bond and its types with examples.

Answer:

Definition: Weak electrostatic attraction between hydrogen and electronegative atoms

Types:

Characteristics:

• Strength: 5-40 kJ/mol
• Requirements: H bonded to F, O, N

Diagram:

Mnemonic: “Hydrogen Needs FON friends” (Fluorine, Oxygen, Nitrogen)

Question 5(B)(2) [4 marks]

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Differentiate between Primary cell and Secondary cell. (Four points)

Answer:

Applications:

• Primary: Remote controls, flashlights
• Secondary: Cars, phones, laptops

Mnemonic: “Primary = Permanent, Secondary = Reversible” (PPSR)

Question 5(B)(3) [4 marks]

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Describe construction, working and chemical equations of lead-acid storage cell with a labelled diagram.

Answer:

Construction:

• Anode: Lead (Pb)
• Cathode: Lead dioxide (PbO₂)
• Electrolyte: Dilute H₂SO₄

Chemical Equations:

• Discharge: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O
• Charge: 2PbSO₄ + 2H₂O → Pb + PbO₂ + 2H₂SO₄

Diagram:

Working: Chemical energy converts to electrical energy during discharge

Mnemonic: “Lead Acid Storage = Reversible Energy” (LASRE)