Alcohols and haloalkanes

Question 1

What is the formula of alcohols?

Answer 1

CnH2n+1OH
Suffix is -ol.

Question 2

What is the polarity of alcohols?

Answer 2

Generally polar due to the electronegative hydroxyl group, which pulls electrons away from the C in the C-OH bond.
The hydroxyl group is also polar.

Question 3

What is the bonding of alcohols?

Answer 3

The partial positive charge on hydrogen in OH attracts lone pairs from oxygen on other molecules, forming hydrogen bonds.
There are weak intermolecular induced dipole dipole interactions.

Question 4

What is the solubility of alcohols?

Answer 4

Small alcohols (up to C4H10) form hydrogen bonds with water, so are soluble.
In larger, most of the molecule is non-polar, so there’s less attraction for polar water.
So as they increase in size, solubility decreases.

Question 5

What is the reactivity of alcohols?

Answer 5

Alcohols form hydrogen bonds with each other.
Very strong, so low volatility and high boiling points.

Question 6

What is substitution reaction of alcohols?

Answer 6

Alcohols react with halide ion compounds (NaBr).
The hydroxyl is replaced by the halide, so the alcohol is transformed into a haloalkane, and forms NaHSO4 + H2O.
The reaction requires an acid catalyst - H2SO4.

Question 7

What is elimination reactions of alcohols?

Answer 7

The useful alkenes can be made by eliminating water from alcohols.
Uses an acid catalyst - concentrated H2SO4 or H3PO4, and heated under reflux.
Sometimes called dehydration as it removes water.

Question 8

What are the products of elimination?

Answer 8

The water molecule forms from the hydroxyl group and a hydrogen from a carbon.
So there’s often two possible alkene product, depending on the side of the hydroxyl group the hydrogen is eliminated.
Sometimes the product has E/Z isomers.

Question 9

What is combustion of alcohols?

Answer 9

Oxidise by burning them, produces carbon dioxide and water.

Question 10

What is combustion of alcohols by acid?

Answer 10

Use the oxidising agent acidified potassium dichromate (VI) (K2Cr2O7) (use H2SO4 to acidify).
Primary alcohols are oxidised to aldehydes, then to carboxylic acids.
Secondary to ketones only.
Tertiary cannot be oxidised.

Question 11

What is the observation of oxidation reactions of alcohols?

Answer 11

The orange dichromate ion is reduced to the green chromium (III) ion (Cr3+).
This can be used to test between tertiary and primary/secondary alcohols.

Question 12

What are aldehydes, ketones, and carboxylic acids?

Answer 12

All have the general formula CnH2nO.
Aldehydes are =O and always on carbon 1, -al.
Ketones are =O and are not on the end carbon -one.
Carboxylic acids have a COOH group at the end chain.

Question 13

What is oxidising primary alcohols to carboxylic acids?

Answer 13

Alcohol is mixed with [O] and heated under reflux.
This can increase the temperature of an organic reaction to boiling without losing volatile solvents, reactants or products.

Question 14

What is oxidising primary alcohols to aldehydes?

Answer 14

Gently heating excess alcohol with a controlled amount of [O] in distillation.
This means the aldehyde (with a lower boiling point than alcohol) is distilled off immediately.

Question 15

What is oxidation of secondary alcohols?

Answer 15

Reflux with acidified potassium dichromate (VI) produces a ketone.

Question 16

What is oxidation of tertiary alcohols?

Answer 16

Tertiary don’t react with [O] so only oxidised by burning them.

Question 17

What is the flammability of alcohols?

Answer 17

Flammability decreases as the chain gets longer, because there’s more bonds to break.
Ethanol is added to petrol.

Question 18

What is volatility of alcohols?

Answer 18

How easily a substance evaporates.
Alcohols are used in perfumes because of their perfect volatility.

Question 19

What are haloalkanes?

Answer 19

An alkane with at least one halogen atom in place of a hydrogen atom.
Prefixes (e.g. bromo-) are placed in alphabetical order.

Question 20

What is the polarity of haloalkanes?

Answer 20

Halogens are more electronegative than carbon, so this bond is polar.
The S+ carbon is electron deficient so can be attacked by a nucleophile.

Question 21

What is a nucleophile?

Answer 21

An electron pair donor - to somewhere with not enough electrons.
e.g. :OH-, H2O:, :NH3

Question 22

What is a nucleophilic substitution reaction of haloalkanes?

Answer 22

A nucleophile attacks a polar molecule, removes the functional group, and attaches where it was.

Question 23

What is hydrolysis of haloalkanes by alkali?

Answer 23

Haloalkanes are hydrolysed by warm aqueous alkali (NaOH or KOH) by nucleophilic substitution reaction.
Forms an alcohol and NaX.

Question 24

What is hydrolysis of haloalkanes with water?

Answer 24

Water is a weak nucleophile so in a much slower reaction will substitute the halogen.
An alcohol is produced again.

Question 25

What is bond enthalpy in hydrolysis?

Answer 25

Weaker carbon-halogen bonds break easier so react faster.
C-F -> C-Cl -> C-Br -> C-I

Question 26

How do you compare hydrolysis rates of haloalkanes?

Answer 26

Add silver nitrate to the mixture, a silver halide precipitate forms.
Time how long it takes for each haloalkane in ethanol to precipitate.
Use paper with a black cross underneath to know when it’s formed.

Question 27

What are chlorofluorocarbons?

Answer 27

Contain only chlorine, fluorine and carbon.
Very stable, volatile, non-flammable and non-toxic.
Previously used in fridges, aerosol cans, dry cleaning and air-conditioning, until scientists realised it destroyed the ozone layer.

Question 28

What is the ozone layer?

Answer 28

A layer of the atmosphere called the stratosphere.
Contains O3.
Absorbs ultraviolet radiation which can cause sunburn or skin cancer.

Question 29

What is the process of natural ozone formation?

Answer 29

O2 + UV –> O + O free radicals
O2 + O –> O3

Question 30

What is the thinning of the ozone layer?

Answer 30

1970s and 80s, scientists discovered the ozone above Antarctica and Artic was thinning very rapidly.
These holes allow more harmful UV radiation to reach the earth.
These are formed when CFCs travel up into the upper atmosphere and absorb high-energy UV radiation.

Question 31

What is the process of ozone thinning?

Answer 31

Initiation: CF2Cl2 + uv –> CF2Cl* + Cl*
Propogation: Cl* + O3 –> O2 + ClO*
ClO* + O* -> O2 + Cl* this is regenerated and attacks another ozone molecule.
O3+O –> 2O2 overall reaction

Question 32

What are nitrogen oxides?

Answer 32

NO* from nitrogen oxides destroy ozone too.
Nitrogen oxides form from aircraft engines, and thunderstorms.

Question 33

How do nitrogen oxides destroy ozone?

Answer 33

NO* + O3 –> NO2* + O2
NO2* + O –> NO* + O2

Question 34

What is the Montreal Protocol 1987?

Answer 34

An international treaty to phase out CFCs and other damaging haloalkanes by the year 2000.
They are only allowed in medical inhalers and fire extinguishers for submarines.

Question 35

What are alternatives to CFCs?

Answer 35

HCFCs - hydrochlorofluorocarbons, and HCFs - hydrofluorocarbons are temporary alternatives until safer products are developed.
CFCs takes around 90 years to leave the atmosphere.
HCFCs take 10-20 years which still damage ozone, but the effect is less.
HFCs don’t affect ozone.

Question 36

What are HFCs with greenhouse gases?

Answer 36

They contribute to the warming of the earth.
Some hydrocarbons are used in fridges, but are still greenhouse gases.
Most aerosols have been replaced by pump spray systems or nitrogen.
Many industrial fridge and freezers use ammonia.
Carbon dioxide is now used as expanded polymers.

Question 37

What is the greenhouse effect?

Answer 37

The earth re-emits any electromagnetic radiation from the sun as infrared radiation (heat).
Various gases in the troposphere absorb some and re-emit in all directions, keeping the earth warm.

Question 38

What are greenhouse gases?

Answer 38

Water vapour, carbon dioxide, methane.
The C=O, O-H and C-H bonds absorb infrared radiation, which makes the bonds vibrate more.
This extra energy is passed on to other molecules by collisions, raising kinetic energy and therefore overall temperature.

Question 39

What is global warming?

Answer 39

Burning fossil fuels, releasing tonnes of carbon dioxide and chopping down trees used for photosynthesis.
Methane levels have risen as food growth increases.
Cows produce large amounts of methane.
Paddy fields where rice is grown also.
All this rises greenhouse gas concentrations, so more heat is trapped and the earth is warmer.

Question 40

What are the consequences of global warming?

Answer 40

Warmer oceans will expand and massive ice sheets could melt, causing sea levels to rise and increase flooding.
The climate depends on a complicated system of ocean currents, winds.
More heat in this system means stormier, less predictable weather.
So there could be less rainfall, with droughts, crop failure, causing famine.
Increased rainfall and flooding could bring diseases like cholera.