Carbon and its Compounds

Correct Option: (b) 7 covalent bonds

Structural formula of ethane:
H H
| |
H - C - C - H
| |
H H

Bond count:
• 1 C-C bond
• 6 C-H bonds (3 on each carbon)
• Total = 7 covalent bonds

Correct Option: (c) ketone

Butanone structure:
CH₃ - C - CH₂ - CH₃
||
O

• Contains carbonyl group (C=O) attached to two carbon atoms
• Ketone functional group suffix: "-one"
• Position: Carbon 2 (butan-2-one)
• Note: Butanal would be aldehyde: CH₃CH₂CH₂CHO

Correct Option: (b) the fuel is not burning completely

Explanation:
• Blackening is due to soot (carbon particles) deposition.
• Soot forms when hydrocarbons undergo incomplete combustion due to:
  1. Insufficient oxygen supply
  2. Blocked air holes in stove
• Complete combustion gives blue flame and CO₂ + H₂O
• Incomplete combustion: CₓHᵧ + (x+y/4)O₂ → xCO + (y/2)H₂O + C(soot)
Solution: Clean stove air holes for proper oxygen supply.

Methyl chloride (CH₃Cl) covalent bond formation:

Electronic configuration:
• Carbon (6): 2,4 (needs 4 electrons)
• Hydrogen (1): 1 (needs 1 electron)
• Chlorine (17): 2,8,7 (needs 1 electron)

Bond formation:
1. Carbon shares 3 electrons with 3 hydrogen atoms → 3 C-H bonds
2. Carbon shares 1 electron with chlorine → 1 C-Cl bond
3. Each shared pair constitutes a covalent bond

H
|
H - C - Cl
|
H

Nature of covalent bond:
• Formed by electron sharing
• Strong bond within molecule
• Low melting/boiling points (intermolecular forces weak)
• Generally poor conductors of electricity

(a) Ethanoic acid (CH₃COOH):
O
||
H : O : C : C : H
|
H

(b) Hydrogen sulphide (H₂S):
H : S : H (S has 6 valence electrons)
or bent structure: H-S-H with two lone pairs on S

(c) Propanone (CH₃COCH₃):
H O H
| || |
H - C - C - C - H
| |
H H

(d) Fluorine molecule (F₂):
: F : F : or : F - F :
(Each F has 7 valence electrons, share one pair)

Homologous series: A family of organic compounds with:

1. Same functional group
2. Similar chemical properties
3. Successive members differ by -CH₂- unit
4. General formula (e.g., CₙH₂ₙ₊₂ for alkanes)
5. Gradation in physical properties with increasing molecular mass

Example: Alkanes (CnH₂n+2)
• Methane: CH₄
• Ethane: C₂H₆ (CH₄ + CH₂)
• Propane: C₃H₈ (C₂H₆ + CH₂)
• Butane: C₄H₁₀ (C₃H₈ + CH₂)

Another example: Alcohols (CnH₂n+1OH)
• Methanol: CH₃OH
• Ethanol: C₂H₅OH
• Propanol: C₃H₇OH
• Butanol: C₄H₉OH

Differentiation tests:

Test	Ethanol (CH₃CH₂OH)	Ethanoic acid (CH₃COOH)
Physical state & smell	Colorless liquid, pleasant smell	Colorless liquid, vinegar smell
Litmus test	No change (neutral)	Turns blue litmus red (acidic)
Sodium bicarbonate test	No reaction	Effervescence (CO₂ gas) CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O
Ester test	Forms ester with acid + conc. H₂SO₄ (fruity smell)	Forms ester with alcohol + conc. H₂SO₄
Iodoform test	Yellow precipitate with I₂ + NaOH	No yellow precipitate

Micelle formation in water:
• Soap molecule has hydrophilic head (-COO⁻Na⁺) and hydrophobic tail (hydrocarbon chain)
• In water, hydrophobic tails cluster together to avoid water
• Hydrophilic heads face outward, interacting with water
• Forms spherical micelles with dirt/oil trapped inside
• Micelles are stabilized by charge repulsion between heads

In ethanol (or other organic solvents):
• No micelle formation
• Ethanol is organic solvent, dissolves both polar and non-polar parts
• Hydrophobic tails don't need to cluster
• Soap molecules remain dispersed individually
• Cleaning action is lost in pure organic solvents

Carbon compounds are excellent fuels because:

1. High calorific value: Release large amount of energy per unit mass
• Example: CH₄ + 2O₂ → CO₂ + 2H₂O + 890 kJ/mol

2. Availability: Abundant in nature (coal, petroleum, natural gas)

3. Ease of storage & transport: Can be stored as solid (coal), liquid (petrol), gas (LPG)

4. Controllable combustion: Burn at controllable rates

5. Versatility: Different forms for different needs:
• Solid: Coal, charcoal
• Liquid: Petrol, diesel, kerosene
• Gas: LPG, CNG, biogas

6. Relatively clean combustion: Complete combustion gives CO₂ + H₂O (non-toxic)

Disadvantages: Non-renewable, cause pollution, greenhouse gases

Scum formation mechanism:

Hard water contains calcium and magnesium salts (chlorides, sulphates, bicarbonates).

Reaction with soap (sodium stearate, C₁₇H₃₅COONa):
1. Soap dissociates: C₁₇H₃₅COONa → C₁₇H₃₅COO⁻ + Na⁺

2. Reacts with Ca²⁺/Mg²⁺ ions:
2C₁₇H₃₅COO⁻ + Ca²⁺ → (C₁₇H₃₅COO)₂Ca ↓ (scum)
2C₁₇H₃₅COO⁻ + Mg²⁺ → (C₁₇H₃₅COO)₂Mg ↓ (scum)

Results:
• Scum is insoluble precipitate of calcium/magnesium stearate
• Soap is wasted until all Ca²⁺/Mg²⁺ ions are precipitated
• Cleaning action starts only after scum formation complete
• Requires more soap for cleaning

Solution: Use detergents (don't form scum) or soften water first.

Observation:

• Blue litmus paper: Remains blue (no change)
• Red litmus paper: Turns blue

Reason:
Soap is basic in nature due to:
1. Soap is sodium/potassium salt of fatty acid
2. Formed by saponification: Fat + NaOH → Soap + glycerol
3. Hydrolysis in water: Soap + H₂O ⇌ Fatty acid + NaOH
4. Produces OH⁻ ions making solution basic (pH 9-10)

Note: This basicity helps in cleaning as it emulsifies oils, but can be harsh on skin.

Hydrogenation: Addition of hydrogen to unsaturated compounds (alkenes/alkynes) in presence of catalyst (Ni, Pd, Pt) at 150-200°C.

General reaction:
R-CH=CH-R' + H₂ → R-CH₂-CH₂-R'
(Unsaturated)            (Saturated)

Example (Vegetable oil to vanaspati ghee):
(C₁₇H₃₃COO)₃C₃H₅ + 3H₂ → (C₁₇H₃₅COO)₃C₃H₅
(Oleic acid甘油酯)            (Stearic acid甘油酯)

Industrial applications:
1. Manufacture of vanaspati ghee: Liquid oils → solid fats
2. Petroleum refining: Improve fuel quality
3. Margarine production: From vegetable oils
4. Organic synthesis: Production of alcohols, amines

Health aspect: Hydrogenated fats contain trans fats, unhealthy for heart.

Hydrocarbons that undergo addition reactions:

• C₃H₆ (Propene) – Alkene with C=C double bond
• C₂H₂ (Ethyne) – Alkyne with C≡C triple bond

Why?
• Addition reactions characteristic of unsaturated hydrocarbons
• Double/triple bonds can open to add atoms (H₂, Cl₂, Br₂, etc.)
• Saturated hydrocarbons (C₂H₆, C₃H₈, CH₄) have only single bonds, undergo substitution not addition

Examples of addition reactions:
1. Hydrogenation: CH₂=CH₂ + H₂ → CH₃-CH₃
2. Halogenation: CH≡CH + 2Br₂ → CHBr₂-CHBr₂
3. Hydration: CH₂=CH₂ + H₂O → CH₃-CH₂OH (with acid)

Bromine water test (or Iodine test):

Procedure:
1. Take two test tubes with butter and cooking oil
2. Add bromine water (reddish-brown) to each
3. Shake well and observe color change

Observations:
• Cooking oil: Bromine water decolorizes (becomes colorless)
• Butter: Bromine water remains reddish-brown (or decolorizes slowly)

Reason:
• Cooking oils are unsaturated (contain C=C bonds) → undergo addition with Br₂
R-CH=CH-R + Br₂ → R-CHBr-CHBr-R
• Butter is saturated (mainly animal fat) → no addition reaction with Br₂

Alternative test: Hydrogenation – Oil becomes solid/semi-solid, butter already solid.

Cleaning action of soap involves three steps:

1. Structure of soap molecule:
• Hydrophilic head: Ionic (-COO⁻Na⁺), water-loving
• Hydrophobic tail: Hydrocarbon chain, water-hating, oil-loving

2. Micelle formation in water:
• Hydrophobic tails cluster together (away from water)
• Hydrophilic heads face outward (toward water)
• Forms spherical aggregates called micelles

3. Cleaning process:
• Grease/dirt (non-polar) gets trapped in micelle center
• Hydrophilic heads keep micelle suspended in water
• Micelles don't coalesce due to charge repulsion
• Rinsing removes micelles with trapped dirt

Visual representation:

Limitation: Doesn't work well in hard water (forms scum).

Electron dot structure of CO₂:

Method 1 (showing all valence electrons):
: O :: C :: O : or : O = C = O :

Method 2 (structural representation):
O = C = O

Explanation:
• Carbon (4 valence electrons) forms double bonds with each oxygen
• Each oxygen (6 valence electrons) shares 2 electrons with carbon
• Carbon achieves octet: 4 from itself + 2 from each oxygen = 8
• Each oxygen achieves octet: 6 from itself + 2 from carbon = 8
• Linear molecule (bond angle 180°)

Note: CO₂ has two C=O double bonds, not single bonds.

Electron dot structure for S₈ (cyclo-octasulphur):

Structure: Crown-shaped ring of 8 sulphur atoms


Bonding:
• Each S atom has 6 valence electrons
• Forms two single bonds with adjacent S atoms
• Each S shares 2 electrons (one with each neighbor)
• Remaining 4 electrons as two lone pairs on each S
• Bond angle S-S-S ≈ 108° (close to tetrahedral)

Simplified representation:
(-S-)₈ with each S having two lone pairs

Pentane (C₅H₁₂) has 3 structural isomers:

1. n-Pentane (straight chain):
CH₃ - CH₂ - CH₂ - CH₂ - CH₃

2. Isopentane (methylbutane, branched):
    CH₃
    |
CH₃ - CH - CH₂ - CH₃

3. Neopentane (dimethylpropane, highly branched):
    CH₃
    |
CH₃ - C - CH₃
    |
    CH₃

Key points:
• Same molecular formula (C₅H₁₂)
• Different connectivity (branching)
• Different physical properties (bp: n-pentane 36°C, iso 28°C, neo 10°C)
• Number of isomers increases with carbon atoms:
  C4: 2 isomers, C5: 3, C6: 5, C7: 9, C8: 18, etc.

The two key properties are:

1. Catenation:
• Ability of carbon atoms to form bonds with other carbon atoms
• Forms chains (straight, branched, cyclic) of various lengths
• Single, double, or triple bonds between carbons
• Very strong C-C bonds (348 kJ/mol)
• Extent much greater than other elements (Si forms only up to 7-8 atom chains)

2. Tetravalency:
• Carbon has 4 valence electrons, needs 4 more for octet
• Can form 4 covalent bonds with other atoms
• Bonds with H, O, N, S, halogens, etc.
• Forms diverse functional groups
• Small atomic size allows strong bonds

Result: Millions of organic compounds (vs. few thousand inorganic).

Cyclopentane:

Molecular formula: C₅H₁₀

Structural formula (pentagonal ring):

or simplified: (CH₂)₅

Electron dot structure:
Each carbon forms:
• 2 single bonds with adjacent carbons
• 2 single bonds with hydrogen atoms
• All bonds are single (saturated)
• Each C has tetrahedral geometry

Note: Cyclopentane is saturated (all C-C single bonds), unlike cyclopentene which has double bond.