Olumawu School Presentation - Alkanes

ALKANES

ORGANIC CHEMISTRY

Multiple Choice

Which of the following factors characterize members of the same homologous series?

• The chemical properties change gradually throughout the series

• Physical properties of members are similar

• They have the same molecular formula

• Successive members undergo changes in molecular by CH₂

Open Ended

Define Hydrocarbon

INTRODUCTION

• These are aliphatic hydrocarbon with general

molecular formula CnH2n+2.

• They are very stable compounds since all four

valence electrons are used up in bonding.

• They are unsaturated organic compounds

containing only carbon and hydrogen atom
joined by single covalent bonds

• The first four members are gases at room

temperature while the next sixteen members
are liquid at room temperature; the higher
members are either semi – solids or solids.

• They are generally prepared by heating

mixture of sodium salt of alkanoic acid and
sodalime.

Draw

Draw the second member of the alkane group.

METHANE – CH4

• It is the major constituent of natural gas and it

is also given off from swamps and marsh gas.

Open Ended

Give other sources of Methane.

Laboratory Preparation of Methane

• It is prepared by reacting soda – lime (quicklime

slaked with conc. NaOH) with sodium ethanoate.
The soda – lime is used because it is not
deliquescent like caustic soda and so does not
attack glass so readily.

•

RCOONa + NaOH

→ R – H + Na2CO3

•

Soda – lime

•

CH3COONa + NaOH

→ CH4 + Na2CO3

•

C2H5COONa + NaOH → C2H6 + Na2CO3

• The CH4 produced is collected over water.

PHYSICAL PROPERTIES

• It is a colourless and odourless gas
• It is slightly soluble in water but soluble in organic

compound.

• It is less dense than air
• It has no action on litmus
• Melting and boiling point increases as their

molecular size increases because as alkane
molecules become bigger, the attractive forces
between the alkane molecules increases.

• Density and flammability increases too.

CHEMICAL PROPERTIES

• Substitution(Chlorination) - Halogenation/Photochemical

Reaction

•

Sunlight/U.V

•

CH4 + Cl2 → CH3Cl + HCl

•

Chloromethane

•

CH3Cl + Cl2 → CH2Cl2 + HCl

•

Dichloromethane

•

CH2Cl2 + Cl2 → CHCl3 + HCl

•

Trichloromethane

•

CHCl3 + Cl2 → CCl4 + HCl

•

Tetrachloromethane

• Substitution reaction involves the direct displacement of an

atom or group by another atom or group. Alkanes are
generally unreactive compared to Alkenes.

USES

• It is a good source of fuel.
• It is used in the industrial preparation of

hydrogen.

• It is used in the preparation of other chemicals

such as carbon (IV)sulphides, alkynes,
trichloromethane(chloroform) and
tetrachloromethane, an organic solvent.

Open Ended

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