Module 4 - Alkanes

Question 1

What is an alkane?

Answer 1

A saturated hydrocarbons containing
C-H bonds only

Question 2

What is the general formula of
an alkane?

Answer 2

CnH2n+2

Question 3

Are alkane bonds polar?
Why/why not?

Answer 3

Nonpolar because carbon and hydrogen
have similar electronegativities

Question 4

What is the shape and angle
of an alkane?

Answer 4

Tetrahedral
109.5°

Question 5

Describe the 𝜎 (sigma) bond in
alkane

Answer 5

The sigma bond is a covalent bond
which has a direct overlap of the electron
clouds of the bonding atoms.

Question 6

What type of intermolecular
forces do alkanes have? Why?

Answer 6

London force → induced dipole-dipole
interaction, because the bonds are
nonpolar

Question 7

What happens to the boiling
point as alkane chain length
increases? Why?

Answer 7

The boiling point increases because there is
more surface area and so more number of
induced dipole- dipole interaction. Therefore
more energy required to overcome the
attraction

Question 8

Does a branched molecule
have lower or higher boiling
point compared to equivalent
straight chain? Why?

Answer 8

The branched molecule has a lower
boiling point because they have fewer
surface area and hence less induced
dipole -dipole interactions.

Question 9

Are alkanes soluble in water?
why?

Answer 9

Insoluble because hydrogen bonds in
water are stronger than alkanes’ London
forces of attraction

Question 10

How reactive are alkanes?

Answer 10

Very unreactive

Question 11

What reactions will alkanes
undergo?

Answer 11

Combustion and reaction with halogens

Question 12

What type of reaction is
combustion?

Answer 12

Oxidation reaction

Question 13

What is complete combustion?

Answer 13

Combustion that occurs with plentiful
supply of air

Question 14

What are the products of
complete combustion when
alkanes are used?

Answer 14

Carbon dioxide and water

Question 15

What is the colour of the
bunsen burner flame during
complete combustion?

Answer 15

Blue flame

Question 16

What is incomplete
combustion and what products
are formed in the case of
alkanes?

Answer 16

Combustion in a limited supply of oxygen
Products : water, carbon dioxide and
carbon monoxide

Question 17

Write an equation for the
complete combustion of
propane

Answer 17

C3H8+ 5O2 → 3CO2+ 4H2O

Question 18

What type of hydrocarbon are
most likely to undergo
incomplete combustion?

Answer 18

Longer chains

Question 19

What is the environmental
impact of carbon monoxide?

Answer 19

It is toxic/poisonous

Question 20

What is the environmental
impact of soot (carbon)?

Answer 20

Asthma, cancer, global dimming

Question 21

How are halogenoalkanes
formed from alkanes?

Answer 21

Radical substitution

Question 22

In the presence of what does
alkane react with halogens?

Answer 22

UV light

Question 23

What are the three stages of
free radical substitution?

Answer 23

Initiation - breaking halogen bond to form free radicals
Propagation - chain part of the reaction where prod s
are formed but free radical remains
Termination - free radicals removed, stable products
formed

Question 24

Write equations for the reaction of CH4 with Cl2 to form CH3Cl

Answer 24

Initiation: Cl2→ 2Cl* (in presence of UV light)
Propagation: Cl* + CH4 → HCl + CH3
CH3 + Cl2 → CH3Cl + Cl
Termination:
CH3 + Cl → CH3Cl
2Cl → Cl2
*CH3+ *CH3→ CH3CH3

Question 25

What is stereoisomerism?

Answer 25

stereoisomers are isomers that have the same composition (that is, the same parts) but that differ in the orientation of those parts in space.

Question 26

Define structural isomer

Answer 26

A structural isomer, also known as a constitutional isomer, is one in which two or more organic compounds have the same molecular formulas but different structures.