Here are the most frequently asked questions in Class 12 Chemistry for Tamil Nadu State Board examinations over the past three years, categorized by chapter:
1. Metallurgy
- Describe various methods of concentrating ores.
- Explain the electrochemical principles of metallurgy.
- What is the significance of the Ellingham diagram in metallurgy?
- Write about the extraction and uses of Aluminium, Zinc, Iron, Copper, and Gold.
2. p-Block Elements (Part I & II)
- Explain the oxidation states of 4d series elements.
- What is lanthanide contraction and its effects?
- Describe the preparation of potassium dichromate.
- Why do zirconium and hafnium exhibit similar properties?
- Compare the ionization enthalpies of first-series transition elements.
3. Coordination Chemistry
- Define coordination compounds and their nomenclature based on IUPAC rules.
- Explain Werner’s theory of coordination compounds.
- Explain the stability of different oxidation states in coordination compounds.
- Explain Crystal Field Theory with examples.
4. Solid State
- What is the difference between crystalline and amorphous solids?
- Explain Schottky and Frenkel defects with examples.
- Calculate the number of atoms in a face-centered cubic (FCC) unit cell.
- Describe the seven crystal systems.
5. Chemical Kinetics
- Derive the rate law expression for first-order and second-order reactions.
- Explain the effect of temperature on reaction rates.
- Explain the significance of the Arrhenius equation.
- Describe the collision theory of reaction rates.
6. Electrochemistry
- What is the Nernst equation? Explain its significance.
- Differentiate between electrochemical and electrolytic cells.
- What is the standard electrode potential? Explain its applications.
- Explain Faraday’s laws of electrolysis.
7. Surface Chemistry
- Explain the differences between physisorption and chemisorption.
- Explain the role of catalysts in surface chemistry.
- What are micelles and their applications?
- Define colloids and describe their classification.
8. Organic Chemistry
- What are electrophilic and nucleophilic substitution reactions? Give examples.
- Explain the mechanism of SN1 and SN2 reactions.
- Write the IUPAC names and structures of given organic compounds.
- Explain the preparation and properties of alcohols and ethers.
9. Carbonyl Compounds and Carboxylic Acids
- Explain the reactivity of aldehydes and ketones.
- Describe the mechanism of the aldol condensation reaction.
- Explain the acidity of carboxylic acids and factors affecting it.
- How do you prepare esters from carboxylic acids?.
10. Biomolecules
- Differentiate between DNA and RNA structures.
- Explain the classification of carbohydrates.
- What are enzymes and their functions in biochemical reactions?
- Describe the different types of proteins and their functions.
11. Chemistry in Everyday Life
- What are drugs and their classification?
- Describe the role of antibiotics, analgesics, and antiseptics.
- What are synthetic polymers and their applications?
- Explain the importance of biodegradable and non-biodegradable polymers.
Answer Guidelines
Detailed answers to the most frequently asked Class 12 Chemistry questions for the Tamil Nadu State Board syllabus.
1. Metallurgy
Q1: Describe various methods of concentrating ores.
Answer:
Ore concentration methods remove impurities and increase the metal content in the ore. Major methods include:
- Gravity Separation: Based on differences in density, used for ores like Gold.
- Magnetic Separation: Used when one component is magnetic (e.g., Fe₃O₄ from gangue).
- Froth Flotation: Used for sulfide ores like ZnS, CuFeS₂. Oil and air bubbles selectively attract ore particles.
- Leaching: A chemical process where an ore is dissolved and precipitated separately, e.g., Aluminium extraction using Bayer’s process.
Q2: Explain the electrochemical principles of metallurgy.
Answer:
Electrochemical metallurgy is used for metal extraction through electrolysis:
- Electrolytic Reduction: Metals like Aluminium (Hall-Héroult process) and Sodium (Down’s process) are extracted from molten salts.
- Electrorefining: Used for refining Copper, Silver, and Gold.
- Electrochemical Series: Determines the feasibility of metal extraction. A metal with a higher reduction potential is more easily reduced.
2. p-Block Elements
Q3: What is lanthanide contraction and its effects?
Answer:
Lanthanide contraction refers to the gradual decrease in atomic and ionic radii of lanthanides due to poor shielding by f-electrons.
Effects:
- Similar chemical properties of Zirconium (Zr) and Hafnium (Hf).
- Increase in ionization energy across the lanthanides.
- High density and hardness of heavy transition metals.
3. Coordination Chemistry
Q4: Explain Werner’s theory of coordination compounds.
Answer:
Werner’s Theory explains the structure of complex compounds:
- Metals exhibit primary valency (oxidation state) and secondary valency (coordination number).
- Secondary valencies are directed towards specific positions in space (octahedral/tetrahedral).
- Example: CoCl₃·6NH₃ → [Co(NH₃)₆]³⁺ Cl₃⁻, where 6 NH₃ molecules are coordinated.
Video Reference for Werner’s Theory
4. Solid State
Q5: Explain Schottky and Frenkel defects.
Answer:
- Schottky Defect: Equal number of cations and anions missing, reducing density. Found in NaCl, KCl, CsCl.
- Frenkel Defect: Cations move to interstitial sites, density remains unchanged. Found in AgCl, ZnS.
5. Chemical Kinetics
6. Electrochemistry
Q7: What is the Nernst equation and its applications?
Answer:
The Nernst equation relates electrode potential to ion concentration:
Applications:
- Determines cell potential under non-standard conditions.
- Used in pH determination using hydrogen electrodes.
Video Reference for Nernst Equation
7. Surface Chemistry
Q8: Differentiate between physisorption and chemisorption.
| Feature | Physisorption | Chemisorption |
|---|---|---|
| Nature | Weak Van der Waals forces | Strong chemical bonds |
| Temperature | Decreases with temp | Increases with temp |
| Reversibility | Reversible | Irreversible |
| Examples | Adsorption of gases on charcoal | Hydrogenation of Nickel |
Video Reference for Physorption and Chemistorption
8. Organic Chemistry
Q9: Explain the mechanism of SN1 and SN2 reactions.
Reference Video for Nucleophilic Substitution Reaction
9. Carbonyl Compounds
Q10: Explain Aldol condensation.
Aldol condensation occurs in aldehydes/ketones with α-hydrogen in base.
Video Reference for Aldol Condensation
10. Biomolecules
Q11: Differentiate between DNA and RNA.
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Strands | Double | Single |
| Bases | A, T, G, C | A, U, G, C |
11. Chemistry in Everyday Life
Q12: What are antibiotics, analgesics, and antiseptics?
- Antibiotics: Kill bacteria (e.g., Penicillin).
- Analgesics: Pain relievers (e.g., Aspirin).
- Antiseptics: Prevent microbial growth (e.g., Dettol).
