Carbon and Its Compounds

Why This Chapter Matters

8-10 marks every board exam. IUPAC naming, homologous series, functional groups, ethanol/ethanoic acid properties, and soaps vs detergents are all tested.

Prerequisites

•Valency: Carbon has valency 4

•Types of bonds: single, double, triple covalent bonds

Core Concepts

1. Why Carbon is Versatile

1.Tetravalency: forms 4 covalent bonds

2.Catenation: C-C bonds possible (chains, branches, rings)

Result: millions of organic compounds.

2. Hydrocarbons

Saturated (Alkanes): CnH2n+2 - only single bonds

CH4 (methane), C2H6 (ethane), C3H8 (propane), C4H10 (butane)

Unsaturated:

Alkenes (C=C double bond): CnH2n - C2H4 (ethene), C3H6 (propene)

Alkynes (C triple C): CnH2n-2 - C2H2 (ethyne), C3H4 (propyne)

3. Functional Groups

-OH (hydroxyl) | -COOH (carboxyl) | -CHO (aldehyde) | C=O (ketone) | -Cl (halide)

4. Homologous Series

Series where each member differs by CH2 (14 mass units).

Same functional group. Same general formula. Gradual property variation.

5. IUPAC Naming

Prefix (carbon count): Meth(1), Eth(2), Prop(3), But(4), Pent(5), Hex(6)

Suffix: -ane (alkane), -ene (alkene), -yne (alkyne), -ol (alcohol), -al (aldehyde), -one (ketone), -oic acid

Examples: CH3OH = Methanol | C2H5OH = Ethanol | CH3COOH = Ethanoic acid

6. Chemical Properties

Combustion: CH4 + 2O2 -> CO2 + 2H2O (complete, blue flame)

Incomplete combustion -> CO + soot (yellow smoky flame)

Substitution (saturated compounds):

CH4 + Cl2 --(sunlight)--> CH3Cl + HCl

Addition (unsaturated compounds):

CH2=CH2 + H2 --(Ni)--> CH3-CH3 (ethane)

Test for unsaturation: Add bromine water -> decolorises (brown to colourless) = unsaturated.

7. Ethanol (C2H5OH)

•Liquid (bp 78 C), miscible with water

•With Na: 2C2H5OH + 2Na -> 2C2H5ONa + H2

•Combustion: C2H5OH + 3O2 -> 2CO2 + 3H2O

•Oxidation: C2H5OH --(K2Cr2O7/H+)--> CH3COOH

8. Ethanoic Acid (CH3COOH / Acetic Acid)

•5-8% solution = vinegar

•Melting point 17 C -> freezes in winter = glacial acetic acid

•Esterification: CH3COOH + C2H5OH ==(H2SO4)==> CH3COOC2H5 + H2O (fruity smell, reversible)

9. Soaps vs Detergents

Soap: Sodium salt of fatty acid (saponification: fat + NaOH -> soap + glycerol)

Does NOT work in hard water (forms scum with Ca2+/Mg2+). Biodegradable.

Detergent: Sodium salt of sulphonic acid.

Works in hard water (Ca/Mg salts are soluble). May not be biodegradable.

Micelle: Soap/detergent in water forms spherical structure with hydrophobic tails inside (around grease) and hydrophilic heads outside (water-facing) -> grease suspended and removed.

PYQs

2023: Names and structures of first two alkynes.

1.Ethyne: HC triple bond CH | 2. Propyne: CH3-C triple bond CH

2022: What is saponification? Write reaction.

Hydrolysis of fat/oil with NaOH. Fat + NaOH -> Soap + Glycerol

2021: Why does carbon form so many compounds?

Catenation (C-C bonds) + Tetravalency (4 bonds possible).

2020: Functional group in CH3CH2CHO and IUPAC name.

Functional group: -CHO (aldehyde). IUPAC name: Propanal.

MCQ Practice

Q1. IUPAC name of CH3COOH:

(A) Methanoic acid (B) Ethanoic acid (C) Propanoic acid (D) Acetic acid

Answer: B

Q2. Unsaturated hydrocarbon:

(A) C2H6 (B) C3H8 (C) C2H4 (D) CH4

Answer: C

Q3 (Hard). Detergents work better in hard water because:

Their Ca/Mg salts are SOLUBLE (unlike soap which forms insoluble scum).

Revision Notes

CARBON: Tetravalency + Catenation = millions of compounds

HYDROCARBONS:
Alkanes CnH2n+2: single bonds only, substitution reactions
Alkenes CnH2n: one C=C, addition reactions
Alkynes CnH2n-2: one C triple C, addition reactions

NAMING: Meth(1) Eth(2) Prop(3) But(4) Pent(5) Hex(6)
+ ane/ene/yne/ol/al/one/oic acid

ETHANOL C2H5OH:
Oxidised to ethanoic acid
Burns cleanly with CO2 and H2O

ETHANOIC ACID CH3COOH:
Vinegar (5-8%)
Esterification: Acid + Alcohol <--> Ester + Water (fruity smell, reversible)

SOAP vs DETERGENT:
Soap: forms scum in hard water (Ca/Mg soaps insoluble)
Detergent: works in hard water (Ca/Mg salts soluble)
Both form MICELLES to remove grease