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Class 10 · Chapter 4 · Chemistry

Carbon and its Compounds Cheat Sheet

Formulae

Alkane (saturated)

CnH2n+2C_nH_{2n+2}

General formula of alkanes; n is the number of carbon atoms. Example: methane CH₄ (n = 1).

Alkene (unsaturated)

CnH2nC_nH_{2n}

General formula of alkenes; the carbon atoms share one double bond. Example: ethene C₂H₄ (n = 2).

Alkyne (unsaturated)

CnH2n−2C_nH_{2n-2}

General formula of alkynes; the carbon atoms share one triple bond. Example: ethyne C₂H₂ (n = 2).

Alcohol

CnH2n+1OHC_nH_{2n+1}OH

General formula of alcohols; the functional group is –OH. Example: ethanol C₂H₅OH.

Carboxylic acid

CnH2n+1COOHC_nH_{2n+1}COOH

General formula of carboxylic acids; the functional group is –COOH. Example: ethanoic acid CH₃COOH.

Reactions

Combustion of methane

CHX4+2 OX2→COX2+2 HX2O\ce{CH4 + 2O2 -> CO2 + 2H2O}

Saturated hydrocarbons burn with a clean blue flame in plenty of air, giving heat and light.

Combustion of ethanol

CX2HX5OH+3 OX2→2 COX2+3 HX2O\ce{C2H5OH + 3O2 -> 2CO2 + 3H2O}

Ethanol is a good fuel and burns with a blue flame to give carbon dioxide and water.

Substitution in methane

CHX4+ClX2→sunlightCHX3Cl+HCl\ce{CH4 + Cl2 ->[sunlight] CH3Cl + HCl}

In sunlight, chlorine replaces hydrogen atoms one by one in a substitution reaction.

Addition of hydrogen (hydrogenation)

CHX2=CHX2+HX2→NiCHX3CHX3\ce{CH2=CH2 + H2 ->[Ni] CH3CH3}

Ethene adds hydrogen in the presence of a nickel catalyst to give ethane; used to make vanaspati ghee from oil.

Oxidation of ethanol

CHX3CHX2OH→alk ⋅ KMnOX4CHX3COOH\ce{CH3CH2OH ->[alk. KMnO4] CH3COOH}

An oxidising agent such as alkaline KMnO₄ oxidises ethanol to ethanoic acid.

Esterification

CHX3COOH+CX2HX5OH→acidCHX3COOCX2HX5+HX2O\ce{CH3COOH + C2H5OH ->[acid] CH3COOC2H5 + H2O}

A carboxylic acid and an alcohol form an ester with a sweet smell; the reaction needs an acid catalyst.

Hydration of ethene

CHX2=CHX2+HX2O→catalystCHX3CHX2OH\ce{CH2=CH2 + H2O ->[catalyst] CH3CH2OH}

Ethene adds water in the presence of a catalyst to form ethanol.

Saponification

CHX3COOCX2HX5+NaOH→CHX3COONa+CX2HX5OH\ce{CH3COOC2H5 + NaOH -> CH3COONa + C2H5OH}

An ester is hydrolysed by a base to give an alcohol and the sodium salt of the acid (soap).

Definitions

Covalent bond
A bond formed by the sharing of electron pairs between atoms.
Catenation
The self-linking property of carbon atoms to form long chains, branched chains and rings.
Tetravalency
The ability of carbon to form four covalent bonds.
Hydrocarbon
A compound made up of only carbon and hydrogen.
Saturated hydrocarbon
A hydrocarbon with only single bonds between carbon atoms, e.g. alkanes.
Unsaturated hydrocarbon
A hydrocarbon with one or more double or triple bonds, e.g. alkenes and alkynes.
Functional group
An atom or group of atoms that gives a family of organic compounds its characteristic properties.
Homologous series
A series of compounds with the same functional group in which successive members differ by a –CH₂– group.
Isomers
Compounds with the same molecular formula but different structures.
Oxidation
Addition of oxygen or removal of hydrogen; converting an alcohol into a carboxylic acid.
Addition reaction
A reaction in which an unsaturated hydrocarbon adds atoms across its multiple bond to become saturated.
Substitution reaction
A reaction in which one atom or group in a molecule is replaced by another.
Esterification
The reaction of an alcohol with a carboxylic acid to form an ester.
Saponification
The hydrolysis of an ester with an alkali to form soap.
Soap
A sodium or potassium salt of a long-chain carboxylic acid.
Micelle
A spherical cluster of soap molecules in water with hydrophobic tails inside and hydrophilic heads outside.
Detergent
A cleansing agent (usually a sodium salt of a sulphonic acid) that works even in hard water.
Denatured alcohol
Ethanol made unfit for drinking by adding poisonous substances such as methanol.
Allotropes
Different forms of the same element with different structures; carbon shows diamond, graphite and fullerene.

Key Points

  • Carbon is tetravalent and forms four covalent bonds; because carbon is small, the bonds are strong and stable.
  • Covalent compounds have weak intermolecular forces, so they have low melting and boiling points and are poor conductors.
  • Saturated hydrocarbons burn with a clean blue flame; unsaturated hydrocarbons burn with a yellow sooty flame due to incomplete combustion.
  • Successive members of a homologous series differ by one carbon and two hydrogen atoms (–CH₂–, mass 14 u).
  • Functional groups: alcohol –OH, aldehyde –CHO, ketone –CO–, carboxylic acid –COOH and halo –X.
  • Ethanol is a liquid at room temperature, miscible with water, and is used in medicines and as a fuel; excess drinking damages the liver.
  • Ethanoic acid (acetic acid) is a weak acid; a 5–8% solution in water is vinegar and pure acid freezes at 290 K (glacial acetic acid).
  • Soap forms micelles that trap oil and dirt, but it does not lather in hard water; detergents work in hard water.