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:
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:
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:
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:
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:
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:
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:
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:
Working: Chemical energy converts to electrical energy during discharge
Mnemonic: “Lead Acid Storage = Reversible Energy” (LASRE)