Alcohols

Question 1

How do alcohols form hydrogen bonds?

Answer 1

Presence of hydroxyl group with its electronegative oxygen atom means that alcohols are polar

Question 2

Why do alcohols have a higher boiling point than alkanes?

Answer 2

Hydrogen bonding

Question 3

Why are alcohols soluble?

Answer 3

Their molecules can form hydrogen bonds with water molecules

Question 4

Why does solubility decrease as size of alcohol molecule increases?

Answer 4

The OH group has less influence and the solubility of the longer hydrocarbon chain becomes more dominant

Question 5

What do alcohols react with oxygen to form (combustion reaction)? What might this reaction be used for?

Answer 5

Carbon dioxide and water, energy released in reaction means that it is sometimes used as fuel

Question 6

What does dehydration mean?

Answer 6

To remove water from a molecule

Question 7

What two acids can be used to dehydrate alcohols?

Answer 7

concentrated H2SO4 or concentrated H3PO4

Question 8

What two molecules are formed when an alcohol is dehydrated?

Answer 8

An alkene and a molecule of water

Question 9

How can alcohols form haloalkanes? What type of reaction is this?

Answer 9

When they react with hydrogen halides, substitution

Question 10

What products are formed when an alcohol reacts with carboxylic acid in the presence of concentrated sulfuring acid? What type of reaction is this?

Answer 10

Esters and water, a type of condensation reaction called esterification

Question 11

What can acidified potassium dichromate be used for?

Answer 11

Acts as an oxidising agent and changes colour from orange to green. This colour change can be used for identifying when an oxidation has taken place and is also test-tube test for primary, secondary alcohols and aldehydes. Primary and secondary alcohols turn the solution to green when oxidised. Tertiary alcohols cannot be oxidised, therefore have no effect

Question 12

What is distillation used for?

Answer 12

Separate a mixture of liquids with different boiling points

Question 13

Describe how distillation is used when testing for primary or secondary alcohols?

Answer 13

A primary alcohol and potassium dichromate is dripped into a warm solution of sulphuric acid. The aldehyde formed is immediately distilled off, which prevents its further oxidation to a carboxylic acid

Question 14

How does the aldehyde that is formed during distillation form a carboxylic acid?

Answer 14

1. Reactants must be heated together under reflux
2. When aldehyde is heated it will vaporise and try to leave the flask
3. Condenser will force the aldehyde to condense and drip back into flask so it cannot escape and will be oxidised to form a carboxylic acid

Question 15

Describe how to perform the distillation of reaction product required practical in 6 steps

Answer 15

1. Reaction mixture is placed into a round bottomed flask
2. Anti bumping granules added - prevents formation of large bubbles when reaction heats up
3. As product is formed it will evaporate, travel up neck of the round bottomed flask into the condenser
4. Thermometer is placed at the neck of the flask to measure the temperature at which product evaporates. This temperature can be used to identify the product or suggest its purity. A pure product will have a sharp boiling point
5. As distillate cools it condenses and travels down the condenser, dripping into collection vessel
6. To prevent evaporation of distillate, collection vessel or distillate can be cooled, by placing beaker in an ice bath