Alkanes

Question 1

What is a hydrocarbon

Answer 1

Compounds which only contain carbon and hydrogen

Question 2

What is a saturated organic compound

Answer 2

One which contains only single bonds between carbon atoms

Question 3

Are alkanes saturated or unsaturated

Answer 3

Saturated (single bonds)

Question 4

What is the prefix for a carbon chain with 1 carbon

Answer 4

Meth-

Question 5

What is the prefix for a carbon chain with 2 carbons

Answer 5

Eth-

Question 6

What is the prefix for the carbon chain with 3 carbons

Answer 6

Prop-

Question 7

What is the prefix for the carbon chain with 4 carbons

Answer 7

But-

Question 8

What is the prefix for the carbon chain with 10 carbons

Answer 8

Dec-

Question 9

What is the general formula for alkanes

Answer 9

CnH2n+2

Question 10

What is a functional group

Answer 10

an atom or group of atoms that gives a compound its characteristic chemical reactivity

Question 11

Do alkanes have a functional group

Answer 11

No

Question 12

Define a homologous series

Answer 12

A series of compounds that have the same functional group and the same general formula, and in which successive members of the series differ by an extra- CH2- unit

Question 13

Do alkanes for a homologous series

Answer 13

Yes

Question 14

What are the types of covalent bonds

Answer 14

• Sigma
• Pi

Question 15

What is a covalent bond

Answer 15

A shard pair of electrons

Question 16

What are the 2 bonds in an alkane that are sigma bonds

Answer 16

C-C and C-H

Question 17

What is a sigma bond

Answer 17

The result of the overlap of 2 orbitals, one from each bonding atom. This bond has 2 shared electrons

Question 18

How many sigma bonds does each carbon have in an alkane

Answer 18

4 sigma bonds

Question 19

In an alkane what is the bond angle around each carbon

Answer 19

109.5 because there are 4 sigma bonds so it’s tetrahedral

Question 20

What process splits crude oil into different fractions

Answer 20

Fractional distillation

Question 21

How is fractional distillation able to separate alkanes into different fractions

Answer 21

Since the alkanes have different boiling points, it increases as their chain length increases

Question 22

Why does the boiling point of alkanes increase

Answer 22

Due to the increased number of London forces, the more London forces the higher the boiling point

Question 23

Why do longer alkanes have a higher boiling point

Answer 23

The molecules have a larger surface area, so more surface contact is possible therefore there are more London forces which then require more energy to overcome

Question 24

Which alkane has a higher boiling point, pentane or 2-methylbutane, and why

Answer 24

Pentane because there is no branching

Question 25

Why do branched alkanes have a lower boiling point than straight chains

Answer 25

Because there are fewer surface points of contact between the molecules, giving fewer London forces

Question 26

What are the 3 reasons that alkanes lack reactivity

Answer 26

- C-C and C-H sigma bonds are strong - C-C bonds are non-polar - The electronegativity of carbon ad hydrogen is so similar that the C-H bond can be considered to be non-polar

Question 27

What are the 2 productions of complete combustion of alkaned

Answer 27

- Carbon dioxide - Water

Question 28

What reaction occurs when there is a limited supply of oxygen when reacting alkanes

Answer 28

Incomplete combustion

Question 29

During incomplete combustion of alkanes what are the 2 possible products other than water

Answer 29

- Carbon monoxide - Carbon (soot)

Question 30

Why is carbon monoxide so toxic

Answer 30

Because it more readily binds to haemoglobin in blood which starves cells of oxygen

Question 31

What type of reaction, reacts alkanes with halogens

Answer 31

Substitution reaction, because a one or hydrogens are substituted for a halogen

Question 32

What is the condition that reacts halogens with alkanes

Answer 32

Sunlight / UV light

Question 33

Name this haloalkane, CH3BR

Answer 33

Bromomethane

Question 34

What are the 3 stages of a radical substitution

Answer 34

- Initiation - Propagation - Termination

Question 35

In a radical substitution, what happens at the initiation stage (use bromine as your example)

Answer 35

The reaction is started when the covalent bond in a bromine molecule is broken by homolytic fission

Question 36

What is homolytic fission

Answer 36

When a covalent is broken and each atom takes of the electrons from the shared pair

Question 37

What happens to bromine during the initiation step in a radical substitution

Answer 37

2 bromine radicals are formed Br.

Question 38

What is a radical

Answer 38

An atom or group of atoms which has an unpaired electron

Question 39

What is the 2nd step in an radical substitution reaction

Answer 39

Propagation

Question 40

What happens during propagation in a radical substitution reaction (Bromine and methane)

Answer 40

- CH4 + Br. -> CH3. + HBr (The bromine radical reacts with the C-H bond in methane forming a methyl radical and a molecule of hydrogen bromide) - CH3. + Br2 -> Ch3Br + Br. (Methyl radical reacts with a bromine molecule forming bromomethane and a new bromine radical)

Question 41

What makes propagation a chain reaction in a radical substitution reaction

Answer 41

Become it reactions continue to occur in a cycle

Question 42

What is the 3rd step in the radical substitution reaction

Answer 42

Termination

Question 43

What happens during termination of radical substitution

Answer 43

2 radicals collide, forming a molecule with all electrons paired

Question 44

What happens when 2 radicals collide

Answer 44

Both radicals are removed from the reaction mixture, stopping the reaction

Question 45

What are the 2 limitation of radical substitution in organic synthesis

Answer 45

- Further substitution - Substitution at different positions in a carbon chain

Question 46

Why is further substitution a limitation to radical substitution

Answer 46

Because the reaction is continuous, more hydrogen can be substituted with halogens so would eventually produce a mixture of different haloalkanes or a compound with no hydrogen in e.g. CH4 -> CH3Br -> CH2Br2 -> CHBr3 -> CBr4

Question 47

Why is substitution at different positions in a carbon chain a limitation to radical substitution

Answer 47

Different products would be formed due to them being isomers