FC16 - Alkanes

Question 1

What are hydrocarbons?

Answer 1

Compounds containing hydrogen and carbon only

Question 2

What is a functional group

Answer 2

An atom or group of atoms that gives a compound its characteristic chemical properties

Question 3

What is a homologous series

Answer 3

A series of compounds that have the same general formula but each successive member differ by an additional CH2 unit

Question 4

What does saturated mean

Answer 4

A compound that contains only single bonds between carbon atoms

Question 5

What does unsaturated mean

Answer 5

A compound that contains at least one double or triple bond between carbon atoms

Question 6

What is the general formula of alkanes?

Answer 6

CnH2n+2

Question 7

Define Alkanes

Answer 7

Saturated hydrocarbon with no specific functional group

Question 8

General formula for a cyclic alkane

Answer 8

CnH2n

Question 9

What does homolytic fission form and describe them

Answer 9

Radicals - species with an unpaired electron

Question 10

Why are radicals so reactive

Answer 10

Because they readily acquire electrons to form non - radicals

Question 11

What does heterolytic fission form

Answer 11

Ions

Question 12

Describe homolytic fission

Answer 12

The breaking of a covalent bond where one electron from the bond remains with one of the atoms and the other electron remains with the other atom that formed the bond

Question 13

Describe heterolytic fission

Answer 13

The breaking of a covalent bond where both electrons forming the bond remain with one atom so the other atom forming the bond loses both forming electrons

Question 14

Why is there a low yield of reactions involving radicals

Answer 14

Radical substitutions lead to many side reactions, these include substitution at different positions on the hydrocarbon and further substitutions. This leads to many different byproducts so the yield of the desired product would be low

Question 15

Define structural isomerism

Answer 15

Compounds with the same molecular formula but different structural formula

Question 16

Define volatility

Answer 16

How readily a liquid vaporises, low boilng point = high volatility

Question 17

Why does more branching of the same isomer result in higher volatility?

Answer 17

More branching means weaker London forces as there is a smaller surface area for contact, and so less energy is needed to overcome these forces therefore higher volatility

Question 18

What products in complete combustion of an alkane

Answer 18

Carbon dioxide + water

Question 19

What products in incomplete combustion of an alkane

Answer 19

Carbon monoxide + water

Question 20

What products in very incomplete combustion of an alkane

Answer 20

’ Carbon + water

Question 21

When does incomplete combustion occur and why is it bad?

Answer 21

When there is limited availability of oxygen. Bad because Carbon monoxide is an odourless, colourless toxic gas that can be fatal in high concentrations

Question 22

Describe simply what happens in the halogenation of alkanes

Answer 22

U.V. Light breaks halogen-halogen bond (not c-h bond as c-h bond is stronger), bi-product is always hydrogen halide, in main product - one H is replaced with halogen

Question 23

Define aliphatic compounds

Answer 23

organic compounds with no benzene ring (C6H6)

Question 24

Define alicyclic compounds

Answer 24

aliphatic compounds with at least one ring of carbon atoms that are not benzene rings

Question 25

Define aromatic compounds

Answer 25

organic compounds with at least one benzene ring

Question 26

What is a benzene ring

Answer 26

cyclic alkane (6 carbons), with 3 double bonds inside (C6H6)