Home
Fullpage
ImpQ

Chapter 4: Carbon and Its Compounds

VIGYAN

Chapter 4: Carbon and Its Compounds

Class X Science

Properties of Carbon

  • Basis of Life: Organic compounds are made up of carbon and form the basis of life of living organisms.
  • Versatile Nature: Carbon is a versatile element; it forms a large variety of compounds because of its tetravalency and the property of catenation.
  • Electronic Configuration: Carbon (Atomic No. 6) has electronic configuration 2, 4. Valency is 4.
  • Bonding: Carbon forms covalent bonds by sharing electrons. It forms bonds with oxygen, sulphur, nitrogen, and chlorine.

Covalent Bond

  • The chemical bond formed by the sharing of electrons from two atoms is known as a covalent bond.
  • Properties:
    • Strong bonds within the molecule, but small intermolecular forces.
    • Low melting and boiling points.
    • Poor conductors of electricity (no charged particles formed).

Unique Features of Carbon

  1. Tetravalency: Carbon has 4 valence electrons. It can bond with four other atoms of carbon or atoms of other monovalent elements.
  2. Catenation: The property of elements to form long chains or branched chains and rings of different sizes. This is due to:
    • Small size of the carbon atom.
    • Unique electronic configuration.
    • Great strength of carbon-carbon bonds.

Allotropy

The phenomenon of the existence of the same element in different physical forms with similar chemical properties is known as allotropy.

  • Crystalline forms: Diamond and Graphite.
  • Amorphous forms: Coal, Charcoal, Lamp black.
  • Fullerenes: Another class of carbon allotropes.

Note: Diamond is a good conductor of heat and a poor conductor of electricity. Graphite is a good conductor of electricity.

Hydrocarbons

Compounds made up of hydrogen and carbon are called Hydrocarbons.

1. Saturated Hydrocarbons (Alkanes)

  • Contain single bonds between carbon atoms.
  • General Formula: \( C_nH_{2n+2} \)
  • Burn with a blue, non-sooty flame.

2. Unsaturated Hydrocarbons

  • Alkenes: Contain double bonds (\( C=C \)). General Formula: \( C_nH_{2n} \)
  • Alkynes: Contain triple bonds (\( C \equiv C \)). General Formula: \( C_nH_{2n-2} \)
  • Burn with a yellow, sooty flame due to incomplete oxidation (high carbon percentage).

Isomers

Organic compounds having the same molecular formula but different structural formulae, and hence different physical and chemical properties. Example: Butane (\( C_4H_{10} \)) has two isomers (n-butane and iso-butane).

[DIAGRAM: Structural isomers of Pentane (n-pentane, iso-pentane, neo-pentane) showing different arrangements of carbon chains]

Heteroatoms & Functional Groups

In a hydrocarbon chain, one or more carbon atoms can be replaced by other atoms (Heteroatoms) like Halogens, Oxygen, Nitrogen, Sulphur. These heteroatoms confer specific properties to the compound and are called functional groups.

  • Halo: -Cl, -Br
  • Alcohol: -OH
  • Aldehyde: -CHO
  • Ketone: -C=O
  • Carboxylic Acid: -COOH

Chemical Properties of Carbon Compounds

1. Combustion

Complete combustion gives carbon dioxide, water, heat, and light.

\[ CH_3CH_2OH(l) + O_2(g) \rightarrow CO_2(g) + H_2O(l) + \text{Heat and Light} \]

2. Oxidation

Carbon compounds are oxidized in the presence of oxidizing agents like alkaline \( KMnO_4 \) or acidified \( K_2Cr_2O_7 \).

\[ CH_3CH_2OH \xrightarrow{\text{Alk. } KMnO_4 \text{ or Acidified } K_2Cr_2O_7} CH_3COOH \]

3. Addition Reaction (Hydrogenation)

Unsaturated hydrocarbons add hydrogen in the presence of catalysts like Nickel (Ni) or Palladium (Pd) to become saturated. Used to convert vegetable oils into vegetable ghee.

\[ CH_2=CH_2 + H_2 \xrightarrow{Ni} CH_3-CH_3 \]

4. Substitution Reaction

In the presence of sunlight, Chlorine replaces hydrogen atoms one by one.

\[ CH_4 + Cl_2 \xrightarrow{\text{Sunlight}} CH_3Cl + HCl \]

Important Carbon Compounds

1. Ethanol (\( C_2H_5OH \))

  • Liquid at room temperature, soluble in water.
  • Active ingredient in alcoholic drinks; used in medicines (tincture iodine, syrups).

Reactions:

  • With Sodium: \( 2Na + 2CH_3CH_2OH \rightarrow 2CH_3CH_2ONa \text{ (Sodium Ethoxide)} + H_2 \)
  • Dehydration: Heating with excess conc. \( H_2SO_4 \) at 443K.
    \( CH_3CH_2OH \xrightarrow{\text{Hot Conc. } H_2SO_4} CH_2=CH_2 + H_2O \)

2. Ethanoic Acid (\( CH_3COOH \))

  • Commonly called Acetic acid. 5-8% solution is Vinegar.
  • Pure ethanoic acid has a melting point of 290 K and freezes in winter, hence called Glacial Acetic Acid.

Reactions:

  • Esterification: Reaction with alcohol to form Ester (sweet-smelling).
    \( CH_3COOH + C_2H_5OH \xrightarrow{\text{Conc. } H_2SO_4} CH_3COOC_2H_5 + H_2O \)
  • Saponification: Esters react with base to give alcohol and sodium salt of acid (Soap).
    \( CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH \)
  • Reaction with Base: \( NaOH + CH_3COOH \rightarrow CH_3COONa + H_2O \)
  • Reaction with Carbonates/Hydrogencarbonates:
    \( 2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + H_2O + CO_2 \)
    \( CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \)

Soaps and Detergents

  • Soap Molecule: Has a hydrophobic tail (hydrocarbon) and hydrophilic head (ionic).
  • Cleansing Action: Forms Micelles where oily dirt is trapped at the center (hydrophobic end) and ionic ends face outward.
  • Hard Water Issue: Soaps react with Calcium and Magnesium salts in hard water to form insoluble scum. Detergents (ammonium or sulphonate salts) do not form scum and work in hard water.

[DIAGRAM: Structure of a Soap Molecule and Micelle formation]

Comparison: Ionic vs Covalent Compounds

Ionic Compounds Covalent Compounds
Formed by complete transfer of electrons. Formed by mutual sharing of electrons.
Generally solids. May exist as solid, liquid, or gas.
High melting and boiling points. Low melting and boiling points.
Soluble in water, insoluble in organic solvents. Generally insoluble in water, soluble in organic solvents.
Conduct electricity in molten/aqueous state. Generally bad conductors of electricity.

Question Bank

Multiple Choice Questions

  1. The following reaction shows the addition of chlorine to methane: \( CH_4 + Cl_2 \xrightarrow{\text{Sunlight}} X \). What is X?
    Ans: (b) \( CH_3Cl + HCl \)
  2. Graphite is used as a lubricant because:
    Ans: (c) It has a high melting point and slippery layers.
  3. The process of addition of hydrogen to an unsaturated compound is called:
    Ans: (d) Addition
  4. Which of the following is an example of an ester?
    Ans: (d) Ethyl acetate
  5. Vinegar is a solution of:
    Ans: (c) 5% - 8% acetic acid in water

Short Answer Questions

Q1. Which substance needs to undergo oxidation to produce acetic acid?
Ans: Ethanol (\( CH_3CH_2OH \)). A sodium bicarbonate test distinguishes them (Ethanoic acid gives brisk effervescence).

Q2. Explain hydrogenation with its industrial application.
Ans: Addition of hydrogen to unsaturated hydrocarbons in the presence of a catalyst (Ni). Used to prepare vegetable ghee from vegetable oils.

Q3. Why is ethyne mixed with oxygen for welding instead of air?
Ans: Burning ethyne with oxygen produces a clean flame with high temperature suitable for welding. Air mixture results in incomplete combustion and a sooty flame with lower temperature.

Q4. Differentiate between soaps and detergents.
Ans: Soaps are sodium salts of fatty acids, biodegradable, but form scum with hard water. Detergents are sodium salts of sulphonic acids, work in hard water, but some are non-biodegradable.

Long Answer Questions

Q1. (a) A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name X and the gas. (b) How to convert Ethanol to Ethene?
Ans:
(a) Salt X is Sodium Ethanoate (\( CH_3COONa \)). Gas is \( CO_2 \). Reaction: \( CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \).
(b) Dehydration using hot conc. \( H_2SO_4 \) at 443K: \( CH_3CH_2OH \xrightarrow{\text{Conc. } H_2SO_4} CH_2=CH_2 + H_2O \).

Q2. What are the characteristics of carbon that result in the vast diversity of carbon compounds?
Ans:
1. Catenation: Self-linking ability to form long chains, branched chains, and rings.
2. Tetravalency: Ability to bond with four other atoms of carbon or other elements.
3. Multiple Bonding: Ability to form double and triple bonds.

Case Study: Carbon Allotropes

Both diamond and graphite are formed by carbon atoms, but they differ in the manner in which the carbon atoms are bonded. Carbon has the unique ability to form bonds with other atoms of carbon (catenation).

Q: Which of the following statements is not correct?
(a) Graphite is much less dense than diamond
(b) Graphite is black and soft
(c) Graphite has low melting point
(d) Graphite feels smooth and slippery
Ans: (c) Graphite has a low melting point (Incorrect, it has a high melting point).

Post a Comment