Question 1 [14 marks]

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

Answer:

Question	Answer	Explanation
(1)	[Ar]4s¹3d¹⁰	Cu has 29 electrons, exception to Aufbau rule
(2)	14	pH + pOH = 14 at 25°C
(3)	cathode	Pure copper deposits at negative electrode
(4)	Cu	Copper forms protective oxide layer
(5)	semi-solid	Peat is partially decomposed organic matter
(6)	Dulong	Dulong's formula calculates calorific value
(7)	Lignite	Lignite has highest moisture (35-75%)
(8)	Poise	SI unit of dynamic viscosity
(9)	High	High flash point prevents ignition
(10)	Emulsion	Oil-water mixture forms emulsion
(11)	Bakelite	Phenol formaldehyde = Bakelite
(12)	S	Sulfur used for vulcanization
(13)	PHBV	PHBV is biodegradable polymer
(14)	volt	EMF measured in volts

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

Question 2(A) [6 marks]

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

List the three importance of pH in various fields.

Answer:

Field	Importance	Application
Medicine	Blood pH maintenance	Normal pH 7.35-7.45 for proper body function
Agriculture	Soil pH optimization	pH 6-7 ideal for crop growth and nutrient absorption
Industry	Quality control	pH affects product quality in food, textiles, pharmaceuticals

Mnemonic: "Medical Agriculture Industry" (MAI)

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

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]

State the factors affecting the rate of corrosion.

Answer:

Factor	Effect	Description
Metal purity	Higher purity = Less corrosion	Impurities create galvanic cells
Temperature	Higher temp = Faster corrosion	Increases reaction rate
Humidity	Higher humidity = More corrosion	Promotes electrochemical reactions

Mnemonic: "Pure Temperature Humidity" (PTH)

Question 2(B) [8 marks]

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

Compare between orbits and orbitals (four points each).

Answer:

Aspect	Orbits	Orbitals
Definition	Fixed circular paths	3D probability regions
Shape	Circular/elliptical	s,p,d,f shapes
Energy	Definite energy levels	Energy ranges
Electron location	Exact position	Probability of finding

Diagram:

    Orbits (Bohr Model)          Orbitals (Quantum Model)
    
         e-                           ∴∴∴∴∴
      ○ ──── ○                       ∴∴∴∴∴∴∴
    ○         ○                    ∴∴∴∴∴∴∴∴∴
      ○ ──── ○                       ∴∴∴∴∴
         +                           ∴∴∴∴∴

Mnemonic: "Definite Shape Energy Location" (DSEL)

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

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

Answer:

Table:

Classification	Type	Example	Description
Source-based	Natural	Coal	Formed naturally
	Artificial	Petrol	Man-made
Physical state	Solid	Wood	Solid at room temp
	Liquid	Diesel	Liquid at room temp
	Gaseous	LPG	Gas at room temp

Mnemonic: "Natural Artificial, Solid Liquid Gas" (NASLG)

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

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]

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

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

Answer:

Component	Definition	Example
Solute	Substance being dissolved	Salt (NaCl)
Solvent	Substance doing the dissolving	Water (H₂O)
Solution	Homogeneous mixture	Salt water

Example: Sugar + Water = Sugar solution

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

Mnemonic: "Solute Solvent Solution" (SSS)

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

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:

Na    →    Na⁺  +  e⁻
Cl + e⁻  →    Cl⁻

Na⁺  +  Cl⁻  →  Na⁺Cl⁻ (NaCl)

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

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

Explain Octane number for gasoline.

Answer:

Aspect	Description
Definition	Measure of fuel's resistance to knocking
Scale	0-100, higher = better anti-knock properties
Standard	n-heptane = 0, iso-octane = 100

Applications: High octane fuel prevents engine knocking, improves performance

Mnemonic: "Octane Opposes Knocking" (OOK)

Question 3(B) [8 marks]

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

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:

    Battery
     ╔═╗
   - ║ ║ +
     ╚═╝
     │ │
  Cathode │ Anode
  (Pure Cu)│(Impure Cu)
     │ │
    ╔═══════╗
    ║CuSO₄  ║
    ║Solution║
    ╚═══════╝

Mnemonic: "Anode Dissolves, Cathode Deposits" (ADCD)

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

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]

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]

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

Explain metal clading for the prevention of corrosion of metals.

Answer:

Aspect	Description
Process	Coating base metal with corrosion-resistant metal
Methods	Hot dipping, electroplating, roll bonding
Examples	Galvanized iron (Zn on Fe), Tin plating

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

Mnemonic: "Coating Protects Metal" (CPM)

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

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:

    Air
────────────────
    Water (O₂ rich)
    ↓ Cathode
────Fe──────────
    ↑ Anode
    Water (O₂ poor)

Mnemonic: "Water Air Interface Corrodes" (WAIC)

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

Explain the working principle of solar cells.

Answer:

Component	Function
Photovoltaic effect	Light energy converts to electrical energy
p-n junction	Creates electric field for charge separation
Electron-hole pairs	Generated when photons hit semiconductor

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

Mnemonic: "Photo Voltaic Junction Creates Current" (PVJCC)

Question 4(B) [8 marks]

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

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:

Moving Surface
╔═══════════════╗
║               ║
║ ∘∘∘∘∘∘∘∘∘∘∘∘∘ ║ ← Boundary layer
║               ║
╚═══════════════╝
Stationary Surface

Mnemonic: "Boundary Barriers Prevent Metal Contact" (BBPMC)

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

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:

    ┌──────────────┐
    │  Oil Bath    │
    │ ┌─────────┐  │
    │ │   Oil   │  │
    │ │Chamber  │  │
    │ └────┬────┘  │
    │      │Orifice│
    │      ▼       │
    │  ┌─────┐     │
    │  │50ml │     │
    │  │Flask│     │
    │  └─────┘     │
    └──────────────┘

Mnemonic: "Redwood Records Time" (RRT)

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

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

Answer:

Term	Definition
Semiconductor	Material with electrical conductivity between conductor and insulator
Insulating material	Material that resists flow of electric current
Elastomer	Polymer with elastic properties, can stretch and return to original shape
Addition polymerization	Monomers join without elimination of small molecules

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

Mnemonic: "Semi Insulating Elastic Addition" (SIEA)

Question 5(A) [6 marks]

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

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]

Describe extrinsic semiconductors and it types with examples.

Answer:

Type	Dopant	Majority Carriers	Example
n-type	Donor atoms (Group V)	Electrons	Si + P
p-type	Acceptor atoms (Group III)	Holes	Si + B

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]

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

Answer:

Property	Thermoplastic	Thermosetting
Structure	Linear/branched chains	Cross-linked network
Heat effect	Softens on heating	Does not soften
Reversibility	Reversible process	Irreversible process
Examples	PVC, PE, PS	Bakelite, Epoxy

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

Question 5(B) [8 marks]

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

Describe hydrogen bond and its types with examples.

Answer:

Definition: Weak electrostatic attraction between hydrogen and electronegative atoms

Types:

Type	Description	Example
Intermolecular	Between different molecules	H₂O···H₂O
Intramolecular	Within same molecule	o-nitrophenol

Characteristics:

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

Diagram:

H₂O···H₂O···H₂O
 │     │     │
δ⁺    δ⁻    δ⁺

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

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

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

Answer:

Aspect	Primary Cell	Secondary Cell
Rechargeability	Non-rechargeable	Rechargeable
Reaction	Irreversible	Reversible
Cost	Low initial cost	High initial cost
Examples	Dry cell, alkaline	Lead-acid, Li-ion

Applications:

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

Mnemonic: "Primary = Permanent, Secondary = Reversible" (PPSR)

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

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:

    ┌─────────────────┐
    │   Pb  │  PbO₂   │
    │ (-)   │   (+)   │
    │Anode  │ Cathode │
    │   │   │   │     │
    │ ┌─────────────┐ │
    │ │   H₂SO₄     │ │
    │ │ Electrolyte │ │
    │ └─────────────┘ │
    └─────────────────┘

Working: Chemical energy converts to electrical energy during discharge

Mnemonic: "Lead Acid Storage = Reversible Energy" (LASRE)