haloalkanes

Question 1

What are haloalkanes

Answer 1

Saturated organic compounds that contain carbon atoms and at least one halogen atom

Question 2

Are halogenalkanes soluble in water?

Answer 2

• yes
• Halogens are more electronegative than carbon so the carbon-halogen bond is polar
• The positive carbon is electron deficient so it can be attacked by a nucleophile

Question 3

Do halogenalkanes have a polar bond? Why?

Answer 3

• Yes contain a polar bond

- Halogen has a higher electronegativity than C so halogen-C bond is polar

Question 4

What type of intermolecular forces do halogens have? Why?

Answer 4

Permanent dipole-dipole and London forces of attraction

C-X bond polarity creates permanent dipoles

Question 5

When would halogenalkanes have higher boiling points?

Answer 5

• Increased carbon chain length

- Halogen further down group 7

Question 6

What is the most important factor in determining halogen reactivity?

Answer 6

The strength of the carbon halogen bond

Question 7

What would bond polarity suggest the order of reactivity would be in haloalkanes?

Answer 7

C-F would be most reactive as most polar bond

Question 8

What would bond enthalpies suggest the order of reactivity would be?

Answer 8

C-I would be most reactive as it has the lowest bond enthalpy

Question 9

What is a primary halogen?

Answer 9

The halogen atom is present at the end of the chain

Question 10

Define nucleophile

Answer 10

Electron pair donor

Question 11

Give 3 examples of nucleophiles

Answer 11

1. OH-
2. CN-
3. NH3

Question 12

What is nucleophilic substitution?

Answer 12

A reaction where a nucleophile donates a lone pair of electrons to a partially positive C atom, the partially negative atom leaves molecule and is replaced by nucleophile

Question 13

What reactant often produces hydroxide ions for hydrolysis?

Answer 13

Water

Question 14

What fission does water undergo to produce OH-

Answer 14

Heterolytic fission

Question 15

What are CFCs?

Answer 15

Chlorine-fluoro-carbons, haloalkanes contains C,F and Cl only

Question 16

What is the problem with CFCs

Answer 16

• Unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution

Question 17

What is the main function of ozone layer

Answer 17

Provides protection from harmful UV radiation

Question 18

How do CFCs break the ozone layer down

Answer 18

Free radical substitution

Question 19

Write an equation for the overall decomposition of ozone into oxygen (O2)

Answer 19

2O3 -> 3O2

Question 20

How do you produce alcohol from haloalkanes

Answer 20

• By a nucleophilic substitution reaction
• Use a warm aqueous alkali like NaOH to hydrolyse the haloalkane to an alcohol
• The reaction has to occur under reflux

Question 21

What is needed for the hydrolyzation of haloalkanes to alcohols

Answer 21

Warm aqueous alkali like sodium hydroxide (NaOH) or potassium hydroxide (KOH)

Question 22

What happens to the reactivity of haloalkenes down group 7?

Answer 22

The reactivity increases

Question 23

What are the properties of chlorofluorocarbons (CFCs)

Answer 23

1. Stable
2. Volatile
3. Non-flammable
4. Non-toxic

Question 24

Why are holes in the ozone layer harmful

Answer 24

Because they allow more harmful UV radiation to each Earth

Question 25

What do free nitrogen oxides radicals do?

Answer 25

NO free radicals from nitrogen oxides destory the ozone

Question 26

How are holes in the ozone layer formed

Answer 26

- CFS in the upper atmosphere absorbs UV radiation and split to form chlorine-free radicals - These radicals catalyze the destruction of ozone, they destroy ozone molecules and are then regenerated to destroy more ozone

Question 27

Describe what alternatives to CFCs are used

Answer 27

- HCFCs and HFCs are being used as temporary alternatives until safer products are developed - Hydrocarbons are used

Question 28

What are the disadvantages of using HCFCs and HFCs as alternatives to CFCs

Answer 28

1. They are broken down in the atmosphere in 10-20 years, they still damage the ozone layer but their damage is smaller than the CFCs 2. HFCs and HCFCs are greenhouse gases

Question 29

What are the advantages of using HFCs over HCFCs

Answer 29

HCFS are also broken down in the atmosphere, unlike HCFCs they don’t contain chlorine so they don’t affect the ozone layer

Question 30

What did the government do to prevent the use of CFCs internationally?

Answer 30

The Montreal Protocol of 1989 phased out the use of CFCs and other ozone-destroying haloalkanes by the year 2000.

Question 31

What is the greenhouse effect

Answer 31

It is when various gases in the atmosphere that contain C=O, C-H or O-H bonds are able to absorb infrared radiation and re-emit it in all directions

Question 32

What are the main greenhouse gases

Answer 32

1. Water vapor 2. Carbon dioxide 3. Methane

Question 33

What do higher concentrations of greenhouse gases due to industrialization mean to global warming?

Answer 33

Higher concentrations of greenhouse gases mean more heat is being trapped and the Earth is getting warmer (global warming)

Question 34

Define global warming

Answer 34

Global warming is responsible for recent changes to climates

Question 35

How are governments working to reduce their greenhouse gas emissions?

Answer 35

- 1997 the Kyoto protocol was signed which means industrialized countries promised to reduce their greenhouse gas emissions to agreed levels, 50% by 2050 - The UK government created policies to use more renewable energy supplies such as wind and solar farms to reduce emission