Alkanes

Question 1

Order of petroleum fractions

Answer 1

1) Petroleum gas
2) Petrol
3) Naphtha
4) kerosene
5) Diesel
6) Lubricating oil
7) Bitumen

Question 2

Use of petroleum gas

Answer 2

Fuel for cooking and heating

Question 3

Uses of petrol

Answer 3

Car fuel

Question 4

Uses of Naphtha

Answer 4

Raw material for making plastics and detergents

Question 5

Uses of kerosene

Answer 5

Fuel for aircraft engines

Fuel for cooking and heating

Question 6

Uses of diesel

Answer 6

Fuel for Diesel engines

Question 7

Uses of lubricating oil

Answer 7

Lubricants for machines, making waxes and polishes

Question 8

Uses of bitumen

Answer 8

Paving road surfaces

Question 9

Name 2 sources of Alkanes

Answer 9

1) crude oil (fractional distillation)

2) natural gas (90% by volume of methane)

Question 10

Structure of Alkanes

Answer 10

Alkanes are saturated hydrocarbons which contain only single covalent bonds

Question 11

Structure of Alkenes

Answer 11

Alkenes are unsaturated hydrocarbons which contain double covalent bonds between carbon atoms

Question 12

What physical properties increase with increase in molecular mass?

Answer 12

1) melting and boiling points
2) density
3) viscosity

Question 13

What physical property decreases with increase in molecular mass?

Answer 13

Flammability

Question 14

Why do melting and boiling points increase as molecular size increases?

Answer 14

Attractive forces (van der waals) between Alkane molecules become stronger as molecules become larger

Question 15

Density of Alkanes

Answer 15

Alkanes are less dense than water, increase as molecular size increases

Question 16

Viscosity of Alkanes

Answer 16

Becomes more viscous (more resistant to flow) as molecular size increases

Question 17

Why does flammability (ability to burn) decrease with increase in molecular size?

Answer 17

Alkanes become less flammable and produce a smokies flame as molecular size increases because percentage of carbon in Alkane molecules increases as molecular size increases

*this reason is only accepted if there is a significant difference in percentage

Question 18

Solubility of Alkanes

Answer 18

Alkanes are insoluble in water (polar reagent) but soluble in organic solvents (eg benzene, ether etc)

Question 19

Physical properties of branched Alkanes (as branching increases)

Answer 19

1) melting and boiling points decrease

2) density decreases

Question 20

Why does melting and boiling point decrease as branching increases?

Answer 20

Branching gives the molecules a more spherical shape leading to lower surface area for van der waals interaction and hence reduces van der waals forces between the molecules.

Question 21

Complete combustion

Answer 21

Forms water and carbon dioxide

Methane + oxygen -> water + carbon dioxide

Question 22

Incomplete combustion

Answer 22

Methane + oxygen -> H20 + CO

Methane + oxygen -> H20 + C

Question 23

Reactivity of Alkanes

Answer 23

Generally unreactive because of strong C-C and C-H bonds

Question 24

What is a substitution reaction?

Answer 24

A reaction in which one or more atoms of an organic compound is replaced by one or more other atoms

Question 25

Describe halogenation

Answer 25

Alkanes react with halogens in the presence of diffused sunlight (Ultra Violet light). A hydrogen atom in the Alkane is replaced by an atom of the halogen (in a substitution reaction)

Question 26

Which halogens are fastest in the rate of reaction of Alkanes?

Answer 26

Fluorine > chlorine > bromine

Question 27

Major product of halogenation

Answer 27

If methane is in excess, major product is chloromethane

If chlorine is in excess, major product is tetra chloromethane

*methane cannot be substituted immediately with4 chlorine atoms to form tetrachloromethane

Question 28

Describe fractional distillation of crude oil

Answer 28

Crude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures.

(Fractions with lowest boiling points condense at the top and fractions with highest boiling points condense at the bottom)