Alkanes Module 4

Question 1

What are Alkanes?

Answer 1

Saturated Hydrocarbons

Question 2

General formula for Alkanes?

Answer 2

C(n)H(2n+2)

Question 3

General formula for cycloalkanes?

Answer 3

C(n)H(2n)

Question 4

What shape are alkane molecules around each Carbon?

Answer 4

Tetrahedral, 4 bonding pairs = 109.5 degrees

Question 5

How is boiling point of alkanes affected by size?

Answer 5

The longer the Carbon chain the higher the boiling point, as the induced dipole-dipole interactions are stronger due to more surface contact and more electrons

Question 6

How does shape affect boiling point of alkanes?

Answer 6

The more branched, the lower the boiling point, as there is less contact area, so induced dipole-dipole interactions are reduced

Question 7

What type of reaction is it, and what is produced when you burn an alkane in Oxygen?

Answer 7

Combustion reaction

Water and CO2

Question 8

What do you get if you burn Alkanes in limited supplies of Oxygen?

Answer 8

Carbon monoxide and water

Question 9

Why is Carbon monoxide poisonous?

Answer 9

Oxygen in bloodstream carried by haemoglobin
Carbon monoxide binds to heamoglobin before Oxygen
Less oxygen can be delivered around the body, leading to Oxygen deprivation

Question 10

What’s bond fission?

Answer 10

Breaking of a covalent bond

Question 11

What’s heterolytic bond fission?

Answer 11

Bond breaks unevenly, with one of the bonded pairs receiving both electrons
A cation (+) and an anion (-) are formed

Question 12

What’s homolytic fission?

Answer 12

Bond breaks evenly, and each bonding pair receives an electron
Two neutral radicals are formed ( have an unpaired electron)

Question 13

What does a halogen + an Alkane?

Answer 13

A haloalkane, called free-radical substitution reaction, and requires ultraviolet light to start

Question 14

What are the 3 stages of free radical substitution?

Answer 14

Initiation
Propagation
Termination

Question 15

What occurs in initiation stage?

Answer 15

Free radicals are produced
Cl2 = (UV light) 2Cl# = photodissocation
So has been split homolytically
#= radical symbol

Question 16

What occurs in propagation stage?

Answer 16

Cl# + CH4 = #CH3 + HCl
#CH3 + Cl2 = CH3Cl + Cl#

Question 17

Termination reactions?

Answer 17

Cl# + #CH3 = CH3Cl
Cl# +Cl# = Cl2
#CH3 + #CH3 = C2H6

Question 18

What’s the problem with free radical substitution?

Answer 18

Produces a mixture of products

Produces many isomers of desired product

Question 19

What’s the best way to reduce a mixture of products from free radical substitution?

Answer 19

Have an excess of your Alkane