Lesson 12: TS Class 10 Physical Science Lesson 12: Carbon and its Compounds - Important Q&A, and Objective Bits

🧪 Telangana Class 10 Physical Science — Lesson 12

Carbon and its Compounds

Complete Chapter Guide: Tetravalency & Catenation, IUPAC Nomenclature Rules, Functional Groups, Esterification & Saponification, Soaps vs. Detergents & Part-B MCQs

📌 Hydrocarbon Homologous Series & General Formulas

1. Alkanes (Saturated − Single Bond)

Hydrocarbons containing single C−C covalent bonds. Suffix: -ane

C_nH_2n+2  (Methane: CH₄ | Ethane: C₂H₆)

2. Alkenes (Unsaturated − Double Bond)

Hydrocarbons containing at least one C=C double bond. Suffix: -ene

C_nH_2n  (Ethene: C₂H₄ | Propene: C₃H₆)

3. Alkynes (Unsaturated − Triple Bond)

Hydrocarbons containing at least one C≡C triple bond. Suffix: -yne

C_nH_2n-2  (Ethyne / Acetylene: C₂H₂)

🧬 IUPAC Nomenclature & Functional Groups Summary

Carbon forms millions of compounds due to its unique properties of Tetravalency (valency = 4) and Catenation (ability to form long carbon chains):

Functional Groups & IUPAC Suffixes At A Glance

1. Alcohol (−OH)

IUPAC Suffix: -ol
Formula: R−OH
Example: Ethanol (C₂H₅OH)

2. Aldehyde (−CHO)

IUPAC Suffix: -al
Formula: R−CHO
Example: Ethanal (CH₃CHO)

3. Ketone (>C=O)

IUPAC Suffix: -one
Formula: R−CO−R'
Example: Propanone / Acetone (CH₃COCH₃)

4. Carboxylic Acid (−COOH)

IUPAC Suffix: -oic acid
Formula: R−COOH
Example: Ethanoic acid / Acetic acid

5. Ester (−COOR)

IUPAC Suffix: -oate
Formula: R−COO−R'
Property: Sweet fruity smell

Carbon Word Roots: C₁ = Meth- | C₂ = Eth- | C₃ = Prop- | C₄ = But- | C₅ = Pent- | C₆ = Hex-.

Comparison: Soaps vs. Synthetic Detergents

Feature	Soaps	Synthetic Detergents
Chemical Nature	Sodium or Potassium salts of long-chain fatty acids (e.g., Sodium Stearate C17H35COONa).	Sodium salts of long-chain alkyl benzene sulphonates or alkyl sulphates.
Action in Hard Water	Ineffective in hard water; forms insoluble sticky white precipitate called Scum with Ca2+ and Mg2+ ions.	Highly effective in both soft and hard water; does not form scum.
Biodegradability	Fully Biodegradable (Environmentally friendly).	Some are Non-biodegradable and cause water pollution.
Cleaning Efficiency	Mild cleansing action.	Strong cleansing action; used in shampoos and washing powders.

📝 Short Answer Questions (2 Marks & 4 Marks)

QUESTION 1 - 2 MARKS

Q1. What is Catenation? Why does Carbon display maximum catenation capacity compared to other elements?

Answer:

• Catenation: The unique property of an element to form strong covalent bonds with other atoms of the same element to construct long straight chains, branched chains, or closed rings.
• Reasons for Carbon's Exceptional Catenation:
  1. Small atomic size of the carbon atom.
  2. Very high Carbon-Carbon (C−C) bond energy (347 kJ/mol), resulting in extremely stable covalent bonds.

QUESTION 2 - 2 MARKS

Q2. What is a Homologous Series? State any two characteristic features of a homologous series.

Answer:

• Homologous Series: A series of organic compounds possessing the same functional group, similar chemical properties, and represented by a general molecular formula.
• Characteristics:
  1. Adjacent members differ by a −CH₂− group in their molecular formula.
  2. Adjacent members differ by 14 u in their molecular mass.
  3. All members exhibit similar chemical properties due to the presence of the same functional group.

QUESTION 3 - 4 MARKS

Q3. What is Esterification? Write a balanced chemical equation for the preparation of Ethyl Acetate (Ester).

Answer:

• Esterification: The chemical reaction in which a Carboxylic Acid reacts with an Alcohol in the presence of a few drops of concentrated Sulfuric Acid (H₂SO₄) as a catalyst to form a sweet fruity-smelling compound called an Ester.
• Chemical Equation:
  CH₃COOH (Ethanoic Acid) + C₂H₅OH (Ethanol) →conc. H₂SO₄→ CH₃COOC₂H₅ (Ethyl Ethanoate) + H₂O
• Use: Esters are used in making perfumes, synthetic flavors, and cosmetics due to their pleasant fruity aroma.

🧮 Chemical Reactions of Carbon Compounds & Micelle Action

4 MARKS - REACTION MECHANISMS

Q4. Explain with balanced chemical equations:
(a) Dehydration of Ethanol to Ethene using conc. H₂SO₄.
(b) Saponification reaction (Preparation of soap).

(a) Dehydration of Ethanol:

When Ethanol is heated at 443 K (170 °C) with excess concentrated H₂SO₄, it loses a water molecule to form Ethene (unsaturated hydrocarbon):

CH₃−CH₂OH →conc. H₂SO₄ at 443 K→ CH₂=CH₂ + H₂O

(b) Saponification Reaction:

When an Ester (like Ethyl Ethanoate) is heated with an aqueous alkali solution like Sodium Hydroxide (NaOH), it converts back into Sodium salt of carboxylic acid (Soap) and Alcohol:

CH₃COOC₂H₅ + NaOH → CH₃COONa (Soap) + C₂H₅OH

✓ Saponification is the fundamental chemical reaction used in soap manufacturing industries.

6 MARKS - ESSAY ON MICELLE FORMATION & CLEANSING ACTION

Q5. Explain the cleansing action of soap with a neat explanation of Micelle formation, Hydrophobic tail, and Hydrophilic head.

Answer:

• Structure of a Soap Molecule (RCOO^-Na⁺): A soap molecule consists of two distinct ends with contrasting solubility properties:
  1. Hydrophobic Tail (Hydrocarbon chain): Water-repelling, non-polar long hydrocarbon tail soluble in oil, grease, and dirt.
  2. Hydrophilic Head (−COO^-Na⁺): Water-attracting, polar ionic head soluble in water.
• Mechanism of Cleansing & Micelle Formation:
  1. When soap is dissolved in water and applied to oily/greasy cloth, the hydrophobic hydrocarbon tails attach themselves to the oily dirt particle.
  2. The ionic hydrophilic heads face outwards toward the surrounding water molecules.
  3. This spherical aggregate structure formed with dirty oil trapped at the center and ionic heads pointing outwards is called a Micelle.
  4. When rinsed with clean water, the water molecules attract the polar heads, pulling the entire micelle along with the trapped oily dirt away from the fabric.

🎯 PART-B Objective Bits Bank (10 MCQs)

BIT 1

1. The general formula for the Alkene homologous series is:

• C_nH_2n+2
• C_nH_2n
• C_nH_2n-2
• C_nH_2n+1

✓ Correct Option: B (C_nH_2n)

BIT 2

2. What is the IUPAC suffix for carboxylic acids?

• -ol
• -al
• -one
• -oic acid

✓ Correct Option: D (-oic acid)

BIT 3

3. The self-linking property of Carbon atoms to form long chains is called:

• Isomerism
• Catenation
• Tetravalency
• Polymerization

✓ Correct Option: B (Catenation)

BIT 4

4. Sweet fruity-smelling organic compounds formed by reacting an acid with an alcohol are called:

• Aldehydes
• Esters
• Ketones
• Ethers

✓ Correct Option: B (Esters)

BIT 5

5. Consecutive members of a homologous series differ in molecular mass by:

• 12 u
• 14 u
• 16 u
• 28 u

✓ Correct Option: B (14 u - corresponding to CH₂)

BIT 6

6. The chemical formula of Ethanoic Acid (Acetic Acid) is:

• HCOOH
• CH₃COOH
• C₂H₅OH
• CH₃CHO

✓ Correct Option: B (CH₃COOH)

BIT 7

7. What is formed when Ethanol is treated with excess concentrated H₂SO₄ at 443 K?

• Ethane
• Ethene
• Ethyne
• Ethanal

✓ Correct Option: B (Ethene CH₂=CH₂)

BIT 8

8. In a soap micelle, the long hydrocarbon tail is:

• Hydrophilic (Water attracting)
• Hydrophobic (Water repelling / Oil attracting)
• Positively charged
• Soluble in water

✓ Correct Option: B (Hydrophobic)

BIT 9

9. Alkaline Potassium Permanganate (Alk. KMnO₄) acts on Ethanol as an:

• Reducing agent
• Oxidizing agent
• Dehydrating agent
• Catalyst

✓ Correct Option: B (Oxidizing agent - converts Ethanol to Ethanoic Acid)

BIT 10

10. The IUPAC name of the first ketone member CH₃COCH₃ (Acetone) is:

• Propanal
• Propanone
• Ethanone
• Butanone

✓ Correct Option: B (Propanone)