NCERT Revision Notes for Chapter 4 Carbon and its Compounds Class 10 Science

Answer

→ Compounds are of two types:

(i) Organic Compounds

(ii) Inorganic Compounds

→ Organic Compounds are made up of Carbons and form the basis of all living organisms.

Answer

→ Carbon always forms covalent bond.

→ The bond formed by sharing of electron pair between two atoms are known as covalent atoms.

• Noble gas configuration of Carbon

→ Carbon is tetravalent, it does not form ionic bond by either losing four electrons (C4+) or by gaining four electrons (C4-). It is difficult to hold four extra electron and would require large amount of energy to remove four electrons. So, carbon can form bond by sharing of its electrons with

the electrons of other carbon atom or with other element and attain noble gas configuration.

→ The atoms of other elements like hydrogen, oxygen and nitrogen, chlorine also form bonds by sharing of electrons.

• H – H single bond between hydrogen atoms (H2)

• O = O double bond between oxygen atoms (O2)

• N ≡ N triple bond between nitrogen atoms

• Water molecule has single covalent bond between one oxygen and two hydrogen atoms.

Answer

The two characteristic properties of carbon element which lead to the formation of large number of compounds :

• Catenation: Carbon can link with carbon atoms by means of covalent bonds to form long chains, branched chains and closed ring. Compound

Carbon atoms may be linked by single, double or triple bonds.

• Tetravalency: Carbon has 4 valence electrons. Carbon can bond with four carbon atoms, monovalent atoms, oxygen, nitrogen and sulphur.

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→ Covalent compounds have low melting and boiling points as they have weak intermolecular force.

→ They are generally poor conductor of electricity as electrons are shared between atoms and no charged particles are formed.

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→ Compounds made up of hydrogen and carbon are called hydrocarbon.

→ There are two types of Hydrocarbons.

(i) Saturated Hydrocarbons

(ii) Unsaturated Hydrocarbons
(i) Saturated Hydrocarbons

→ Single bond between carbon atoms.

→ ㅡCㅡCㅡ

→ Alkanes are saturated hydrocarbons.

General Formula: CnH2n+2

Electron Dot Structure of Saturated Hydrocarbons

• Ethane C2H6

Names, molecular formulae and structure formulae of saturated hydrocarbons (Alkanes):

Answer

(i) Straight (unbranched) chain

Example: C3H8

ㅡCㅡCㅡCㅡCㅡCㅡ

(ii) Branched

→ These three above compounds has same molecular formula but different structures are called structural isomers and phenomenon is structural isomerism.

(iii) Cyclic

Example: C6H12

Answer

→ In hydrocarbon chain, one or more hydrogen atom is replaced by other atoms in accordance with their valancies. These are heteroatom.

→ These heteroatom or group of atoms which make carbon compound reactive and decides its properties are called functional groups.

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→ It is series of compounds in which the some functional group substitutes for the hydrogen in a carbon chain.

Example: Alcohols – CH3OH, C2H5OH, C3H7OH, C4H9OH

• They have same general formula.

• Any two homologues differ by – CH2 group and difference in molecular mass is 14µ.

• They have same chemical properties but show gradual change in physical properties.

Nomenclature of Carbon Compounds

(i) Identify the number of carbon atoms in compounds.

(ii) Functional group is indicated by suffix or prefix.

Answer

(i) Combustion

• Carbon and its compounds are used as fuels because they burn in air releasing lot of heat energy.

• Saturated hydrocarbon generally burn in air with blue and non-sooty flame.

• Unsaturated hydrocarbon burns in air with yellow sooty flame because percentage of carbon is higher than saturated hydrocarbon which does not get completely oxidized in air.

(ii) Oxidation

Alcohols can be converted to carboxylic acid in presence of oxidizing agent alkaline KMnO4 (potassium permangnate) or acidic potassium dichromate.

(iii) Addition Reaction

Unsaturated hydrocarbon add hydrogen in the presence of catalyst palladium or nickel. Vegetable oils are converted into vegetable ghee using this process. 

It is also called hydrogenation of vegetable oils.

(iv) Substitution Reaction

Answer

Physical Properties of Ethanol

• Colourless, pleasant smell and burning taste.

• Soluble in water.

• Volatile liquid with low boiling point of 351 K.

• Neutral compound.

Chemical Properties of Ethanol

(i) Reaction with Sodium

2Na + CH3CH2OH → 2CH3CH2ONa+ + H2

                                   (Sodium ethoxide)

This reaction is used as a test for ethanol by evolution of H2 gas (Burn with pop sound).

(ii) Dehydration

Physical Properties of Ethanoic acid

• Colourless liquid having sour taste and have smell of vinegar.

• Boiling point is 391 K.

• When pure CH3COOH is freezed, it forms colourless ice like solid. So it is called glacial acetic acid.

Chemical Properties

(i) Esterification

Sweet smelling ester is formed.

This is saponification as soap is prepared by this.

(ii) Reaction with base

NaOH + CH3COOH → CH3COONa + H2O

(iii) Reaction with carbonates and hydrogen carbonates :

2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2

CHH2COOH + NaHCOH2 → CH3COONa + H2O + CO2

Answer

• Soap is sodium or potassium salt of long chain carboxylic acid. Example: C17H35COONa+

• Soaps are effective only in soft water.

• Detergents are ammonium or sulphonate salt of long chain of carboxylic acid.

• Detergents are effective in both hard and soft water.

Soap molecule has following parts:

(i) Ionic (hydrophilic) part

(ii) Long hydrocarbon chain (hydrophobic) part

Cleansing Action of Soap

• Most dirt is oily in nature and hydrophobic end attaches itself with dirt and the ionic end is surrounded with molecule of water. This result in formation of a radial structure called micelles.

• Soap micelles helps to dissolve dirt and grease in water and cloth gets cleaned.

• The magnesium and calcium salt present in hard water react with soap molecule to form insoluble product called scum. This scum create difficulty in cleansing action.

• By use of detergent, insoluble scum is not formed with hard water and cloths get cleaned effectively.