Module 4: Haloalkanes (Chapter 15)

Question 1

Define haloalkane

Answer 1

Compound containing only carbon, hydrogen and at least one halogen

Question 2

Describe the reactivity of haloalkanes

Answer 2

The halogens in the C-X bond are more elctronegative than carbon, making the bond polar. Down the group reactivity increases due to a smaller difference in electronegativity, so less attraction of a pair of electrons to the halogen atom. Easier to break the bonds further down the group due to a weaker bond enthalpy.

Question 3

Defie nucleophile

Answer 3

Electron pair donator

Question 4

How are haloalkanes formed?

Answer 4

Nucleophilic substitution

Question 5

Define hydrolysis

Answer 5

A process of decomposition whereby a molecule of water is added to break a bond

Question 6

Hydrolysis of a haloalkane

Answer 6

-OH nucleophile approaches the carbon atom attached to a halogen from behind
This direction minimises repulsion between the nucleophile and S+ carbon atom
A lone pair of electrons on the -OH ion is attracted and donated to the carbon
A new bond is formed between oxygen and carbon.
C-X bond breaks by heterolytic fission
Alcohol product

Question 7

Reactants and product of hydrolysis

Answer 7

NaOH (aq) and reflux

Formation of an alcohol

Question 8

Changing rate of hydrolysis with bond enthalpy of halogens

Answer 8

Weaker bond enthalpy down the halogens, so more reactive down the group and a faster rate of hysrolysis. C-I faster than C-Cl

Question 9

How can the rate of hydrolysis be measured?

Answer 9

Add ethanol or any other alcohol to the haloalkanes
Heat in a water bath and include a test tube of silver nitrate as well
Add the silver nitrate to each sample using a stop clock to measure time taken
Observe and record time taken for a preciptate to form

Question 10

Colours of halogen precipitates

Answer 10

Chloride = white 
Bromide = cream
Iodide = yellow

Question 11

Purpose of the ozone

Answer 11

Protects the Earth from the shorter wavelength UV which is very damaging, by absorbing it.

Question 12

What harm could the UV causes to humans?

Answer 12

Severe sunburn and genetic damage e.g. cancer

Question 13

Uses of organohalogens

Answer 13

Pesticides, propellants in aerosols, refridgerants, solvents, flame retardents
Called CFC’s

Question 14

Role of radicals in destriction of the ozones

Answer 14

CFC’s broken by UV rays into radicals e.g. Cl and NO
Free radicals are catalysts, reacting with the ozone to form intermediates and break the ozone into oxygen
O3+O = 2O2

Question 15

NO radical as a different natural radical

Answer 15

Naturally found in lightening strikes and from aircraft

Result in the same formation of oxygen