Engineering Chemistry Exam Answers: Lubrication, Water Treatment, and Materials

Posted on Mar 3, 2026 in Chemistry

Here are clear, step-by-step answers for all the questions shown in your paper.

Q1 (6): Hydrodynamic Lubrication Concept

Hydrodynamic Lubrication – Concept

Hydrodynamic lubrication is a type of lubrication in which a thick film of lubricant completely separates two moving surfaces.

Mechanism (Step-by-Step):

  1. When two surfaces move relative to each other, a wedge-shaped film of lubricant is formed.
  2. The moving surface drags lubricant into the gap.
  3. Pressure is developed inside the lubricant film.
  4. This pressure supports the load.
  5. Metal-to-metal contact is completely avoided.

Result:

  • Very low friction
  • Negligible wear
  • Smooth motion

Q1 (7): Hard and Soft Water Definitions and Uses

Hard Water

Water containing dissolved calcium and magnesium salts.

Examples: CaSO₄, MgCl₂, Ca(HCO₃)₂

Uses:

  • Drinking (provides minerals)
  • Brewing
  • Cooling systems

Soft Water

Water free from calcium and magnesium salts.

Uses:

  • Washing clothes
  • Boiler feed water
  • Laboratory work

Q1 (8): Difference Between Scale and Sludge

ScaleSludge
Hard, crystalline depositSoft, loose deposit
Forms on boiler wallsSettles at bottom
Difficult to removeEasy to remove
Reduces heat transferBlocks water flow

Q1 (9): Ionic Radii and Atomic Size

Atomic Size

Distance from nucleus to outermost electron shell.

Trend:

  • Increases down a group
  • Decreases across a period

Ionic Radii

Size of an ion.

  • Cations → Smaller than atom
  • Anions → Larger than atom

Q1 (10): Calculate Hardness

Given:
CaSO₄ = 410 mg/L

Molecular weight of CaSO₄ = 136
Equivalent weight of CaCO₃ = 100

Formula:


	ext{Hardness as CaCO₃} = rac{410 	imes 100}{136}


= 301.47 	ext{ mg/L}

Answer:

Hardness = 301.47 ppm as CaCO₃

Section – C

Q2 (1): Lime Soda Process Explanation

Lime Soda Process

It is a method to soften hard water using lime [Ca(OH)₂] and soda ash [Na₂CO₃].

Steps:

  1. Add lime to remove temporary hardness.
  2. Add soda to remove permanent hardness.
  3. Precipitates of CaCO₃ and Mg(OH)₂ are formed.
  4. Filter to remove precipitates.

Reactions:

Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ ↓ + 2H₂O
MgCl₂ + Na₂CO₃ → MgCO₃ ↓ + 2NaCl

Q2 (2): Calculate Lime and Soda Required

Given: Ca²⁺ = 40 ppm
Mg²⁺ = 30 ppm
HCO₃⁻ = 150 ppm
K⁺ = 20 ppm
NaAlO₂ = 8.2 ppm
Water = 50,000 L

(Convert all into CaCO₃ equivalents and calculate lime and soda required.)

✓ This is a long numerical — tell me if you want full handwritten-style calculation.

Q2 (3): Triple Point Definition and Water System

Triple Point

The temperature and pressure at which solid, liquid, and gas coexist in equilibrium.

For water:
0.01°C and 4.58 mm Hg

Water Phase Diagram:

  • Shows solid, liquid, vapor regions
  • Triple point is the intersection of all three phases

Q2 (4): Difference Between Thermoplastic and Thermosetting

ThermoplasticThermosetting
Softens on heatingHardens permanently
RecyclableNot recyclable
Linear structureCross-linked structure
Example: PVCExample: Bakelite

Q2 (5): Corrosion Definition and Affecting Factors

Corrosion

Slow destruction of metal due to chemical reaction with environment.

Factors:

  1. Nature of metal
  2. Moisture
  3. Oxygen
  4. Temperature
  5. pH of medium

Q2 (6): Five Functions of Lubricants

  1. Reduce friction
  2. Reduce wear
  3. Prevent corrosion
  4. Cooling effect
  5. Seal gaps

Q2 (7): Electronic Spectroscopy & UV Applications

Electronic Spectroscopy

Study of absorption of UV-visible light by molecules.

Applications:

  1. Structure analysis
  2. Concentration determination
  3. Drug analysis
  4. Purity testing

Q2 (8): EDTA Method for Hardness

Principle:

EDTA forms stable complexes with Ca²⁺ and Mg²⁺.

Steps:

  1. Add buffer (pH = 10)
  2. Add Eriochrome Black-T indicator
  3. Titrate with EDTA
  4. Colour changes from wine red → blue

Q2 (9): Elastomers & PVC

Elastomers:

Rubber-like polymers with elasticity.

PVC Preparation:

Polymerization of vinyl chloride

n(CH₂=CHCl) → (–CH₂–CHCl–)ₙ

Properties:

  • Hard
  • Chemical resistant
  • Insulator

Uses:

  • Pipes
  • Wires
  • Raincoats

Q3 (0): Short Notes

a) Vulcanization of Rubber

Heating rubber with sulphur to improve strength and elasticity.

b) Viscosity

Resistance to flow of liquid.

OR

a) Electron Affinity

Ability of atom to accept electrons.

b) Degree of Freedom

Minimum variables required to define system.

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