Nature’s Chemistry #1: Homologous Series

Question 1

What is a homologous series?

Answer 1

A family of compounds with the same general formula and similar chemical properties that show a gradual change in physical properties

Question 2

Hydrocarbon

Answer 2

Molecules which consist of hydrogen and carbon atoms only

Question 3

Molecular formula

Answer 3

Formula which shows the number of atoms of the different elements which are present in one molecule of a substance
(Eg H2O)

Question 4

Full structural formula

Answer 4

A 2D drawing of a 3D molecule. It shows the atoms present and the position of a covalent bond.

Question 5

Shortened structural formula

Answer 5

Shows the position of the atoms in the molecules without showing the bonds

Question 6

Alkanes summary

Answer 6

• subset of Saturated hydrocarbons
• end in -ane
• only contain carbon to carbon single bonds
• general formula CnH2n+2
• all insoluble in water
• commonly used as fuels

Question 7

Alkanes end in…

Answer 7

-ane

Question 8

Isomer

Answer 8

Molecules which have the same molecular formula but different structural formula

Question 9

Isomer pitfalls

Answer 9

• flipping it (if given an isomer with branch above, don’t just draw one with branch below)
• drawing the branch nearer the right hand side of the molecule stead of the left
• drawing a bend in the longest chain

Question 10

Physical property

Answer 10

Something that can be observed or measured

Question 11

As the number of carbon atoms increases…

Answer 11

the boiling point increases

Question 12

As the size of the molecule increases,

Answer 12

The size of force of attraction also increases

Question 13

What does it mean that alkanes have more intermolecular forces the bigger the molecule?

Answer 13

More energy is required to overcome the forces and convert the liquid into a gas

Question 14

Chemical property

Answer 14

A property that becomes evident during a chemical reaction

Question 15

Flammability

Answer 15

Ease of combustion

Question 16

As the chain length increases…

Answer 16

Flammability decreases

Question 17

Why are smaller alkanes more flammable?

Answer 17

They can mix with oxygen in the air

Question 18

How do alkanes undergo combustion?

Answer 18

With oxygen in the air

Question 19

What are the products of combustion?

Answer 19

Carbon dioxide, water

Question 20

Testing for the products of combustion

Answer 20

CO2
- turns limewater milky

WATER
- turns cobalt chloride from blue to pink
- melts at 0°C
- boils at 100°C

Question 21

Alkanes: Complete combustion

Answer 21

In a plentiful supply of oxygen, alkanes burn to produce only carbon dioxide and water

Question 22

Alkanes: incomplete combustion

Answer 22

In a limited supply of oxygen, alkanes burn to produce carbon, carbon monoxide, and water

Question 23

Saturated hydrocarbons

Answer 23

A hydrocarbon in which all carbon to carbon covalent bonds are single bonds

Question 24

The effect of saturation on alkanes

Answer 24

Relatively unreactive, with the exception of combustion

Question 25

Uses of hydrocarbons

Answer 25

Gasoline (Petroleum): fuel for cars Naphtha: Making chemicals

Question 26

General formula of cycloalkanes

Answer 26

CnH2n

Question 27

Physical properties of cycloalkanes

Answer 27

- as the cycloalkanes increase in size, their MP and BP increase - as the size of the molecule decreases, the number of intermolecular forces decreases - so, the amount of energy required to break the intermolecular forces increases

Question 28

Chemical properties of cycloalkanes

Answer 28

- saturated hydrocarbons - this saturation makes them relatively un reactive, with the exception of combustion - cycloalkanes burn to produce carbon dioxide and water

Question 29

Uses of cycloalkanes

Answer 29

- cycloalkanes are immiscible in water. They are good solvents for other compounds that are soluble in water - used to make other compounds (main use of cyclohexane is to make nylon)

Question 30

How do you separate cycloalkanes?

Answer 30

Separating funnel

Question 31

What does it mean that cycloalkanes are immiscible in water?

Answer 31

Therefore the are good solvents for other compounds that are insoluble in water

Question 32

Alkenes summary

Answer 32

- a homologous series of unsaturated hydrocarbons - all end in ene - contain a reactive carbon to carbon double bond - CnH2n - used to make polymers and alcohols - are insoluble in water

Question 33

Unsaturated hydrocarbon

Answer 33

Hydrocarbon with at least one c=c

Question 34

How to test for an unsaturated hydrocarbon (alkene, cycloalkene)

Answer 34

Decolourised bromine water

Question 35

What do saturated hydrocarbons not do?

Answer 35

- undergo addition reactions - decolourise bromine water

Question 36

What do unsaturated hydrocarbons do?

Answer 36

- undergo addition reactions - decolourise bromine water

Question 37

What does it mean that the double bond in the alkane is very reactive?

Answer 37

It can break and other atoms can add onto the molecule

Question 38

6 addition reactions

Answer 38

- bromination - hydration - hydrogenation - chlorination - iodonation - flouronation

Question 39

Alkane + bromine

Answer 39

Dibromoalkane

Question 40

Ethene + bromine

Answer 40

1,2 - dibromoethane

Question 41

Alkene + hydrogen

Answer 41

Alkane

Question 42

Ethene + hydrogen

Answer 42

Ethane

Question 43

Alkanes are … in water

Answer 43

Insoluble

Question 44

Alkenes are used to make

Answer 44

Alcohols and polymers