TOPIC 3/4: Basic Concepts of Organic Chemistry + Alkanes

Question 1

Define: aliphatic

Answer 1

Carbon atoms joined to each other in unbranched or branched chains

Question 2

Define: alicyclic

Answer 2

Carbon atoms joined to each other in a cyclic structure

Question 3

Define: aromatic

Answer 3

Some/All of the carbon atoms are found in a benzene ring

Question 4

Define: homologous series

Answer 4

a series of organic compounds with the same functional group which undergo similar chemical reactions

Question 5

Describe the structural difference between aliphatic and aromatic organic molecules

Answer 5

• aliphatic: carbon atoms joined together in straight, branched chains
• aromatic: contain 1 or more benzene rings

Question 6

State the three main types of reaction mechanisms

Answer 6

• addition
• substitution

-elimination

Question 7

Explain how branching affects boiling point

Answer 7

More branching means that there is less surface area contact between adjacent molecules which leads to less London forces and so less energy is required to overcome them which leads to a lower boiling point

Question 8

Explain how chain length affects boiling point

Answer 8

As chain length increases, surface area contact increased between adjacent molecules which leads to more London forced which require more energy to overcome, therefore increasing the boiling point

Question 9

Define: structural isomer

Answer 9

same molecular formula but different structural formulae

Question 10

Why can alkanes not reaction with halogens unless in the presence of UV light?

Answer 10

high bold enthalpy of the C-C bond

Question 11

State the difference between complete and incomplete combustion

Answer 11

Complete:
- occurs in excess supply of oxygen to form: CO2 & H2O

Incomplete:
- occurs in limited supply of oxygen to form: CO & H2O

Question 12

Suggest what might be observed to show that carbon is being formed

Answer 12

a sooty flame

Question 13

State why carbon monoxide can cause dizziness, fainting, loss of consciousness and death in humans

Answer 13

CO irreversibly bings to haemoglobin instead of oxygen

Question 14

State two reasons why alkanes are unreactive

Answer 14

• high bond enthalpy of C-C & C-H bonds
• very low polarity of sigma bonds present

Question 15

Define: radical

Answer 15

A species with an unpaired electron

Question 16

State the conditions for initiation

Answer 16

• UV radiation
• High temperatures (400°C)

Question 17

Define: functional group

Answer 17

The part of the organic molecule that is largely responsible for the molecule’s chemical properties

Question 18

State the difference between homolytic and heterolytic fission

Answer 18

Homolytic:
- when covalent bond breaks, each bonded atom takes one of shared pair electrons from bond

Heterolytic:
- when covalent bond breaks, one bonded atom takes both electrons from bond

Question 19

General formula for cycloalkanes

Answer 19

CnH2n

Question 20

How do you calculate molecular formula

Answer 20

Molecular mass / Mr

Question 21

Define: electrophile

Answer 21

Electron pair acceptor (Br2)

Question 22

Define: nucleophile

Answer 22

Electron pair donor (OH-)

Question 23

Define: unsaturated

Answer 23

A compound with a carbon to carbon multiple bond

Question 24

define: saturated hydrocarbon

Answer 24

contains only carbon and hydrogen atoms joined together by single covalent bonds

Question 25

how do you calculate volume of a gas at room temperature

Answer 25

vol at RTP = mol x 24

Question 26

what do curly arrows represent?

Answer 26

the movement of a pair of electrons

Question 27

State the three different types of structural isomerism. (3)

Answer 27

• chain isomerism
• positional isomerism
• functional group isomerism

Question 28

State the bond angle in an alkane molecule

Answer 28

109.5 oC

Question 29

State, with a reason, whether the boiling point of ethyne would be expected to be higher or lower than the boiling point of ethane. (2)

Answer 29

• ethyne has fewer electrons than ethane
• the intermolecular forces would be weaker, so the b.p. would be lower

Question 30

Explain why carbon monoxide is dangerous if inhaled. (2)

Answer 30

• CO binds to haemoglobin which therefore cannot bind to oxygen
• carbon dioxide cannot be removed from the body