Alcohols (14)

Question 1

What is the functional group and general equation of alcohols?

Answer 1

OH (hydroxyl group) is the functional group and the general equation is CnH(2n+1)OH

Question 2

What is methanol used for?

Answer 2

Methanol is used as a high performance fuel because of its efficient combustion. It’s also a chemical feedstock which means its a good starting material for many polymers.

Question 3

What are the physical properties of alcohols like compared to alkanes?

Answer 3

Alcohols have higher melting points, a greater solubility in water and are less volatile which means they don’t convert from a liquid to a gas as easily as alkanes.

Question 4

Why are the physical properties of alcohols different to alkanes?

Answer 4

Alkanes have non-polar bonds as the electronegativity between carbon and hydrogen is very similar. The intermolecular forces that form between them are very weak and easily broken. Alcohols also have non-polar bonds but they also have a polar OH group because of the difference in electronegativity between the hydrogen and oxygen which means they can form hydrogen bonds that are harder to overcome.

Question 5

Why are alkanes more volatile than alcohols?

Answer 5

Alcohols have the OH groups which means they form hydrogen bonds that require more energy to overcome than the weak intermolecular forces in alkanes. This means it’s harder to break the bonds in alcohols and make them into a gas from a liquid

Question 6

What happens to the properties of alcohols vs alkanes as the carbon chain increases?

Answer 6

As the chain increases in size, the influence of the OH group becomes smaller and so the solubility decreases as there are more hydrocarbons.

Question 7

What are primary alcohols?

Answer 7

An alcohol with the OH group attached to a carbon that has 2 hydrogens attached and 1 R-group.

Question 8

What are secondary alcohols?

Answer 8

An alcohol with an OH group attached to a carbon that has 1 hydrogen and 2 R-groups

Question 9

What are tertiary alcohols?

Answer 9

An alcohols with an OH group attached to a carbon with 3 R-groups and no hydrogen

Question 10

What reaction do primary and secondary alcohols undergo?

Answer 10

Oxidation reactions

Question 11

What is the oxidising agent that is used for oxidising alcohols?

Answer 11

Acidified potassium dichromate. K2Cr2O7 acidified with H2SO4

Question 12

What happens to the oxidising agent if the alcohol is oxidised?

Answer 12

The acidified potassium dichromate solution will turn from orange to green. This is because of dichromate ions becoming chromium (III) ion.

Question 13

What products can be made from the oxidation of primary alcohols?

Answer 13

Aldehyde or carboxylic acids

Question 14

How do you prepare an aldehyde from an alcohol?

Answer 14

You use a primary alcohol and add the acidified potassium dichromate which turns from orange to green. To ensure an aldehyde is made, a distillation will have to occur to make sure the aldehyde is distilled as the reaction mixture forms.

Question 15

Describe the process of making an aldehyde from an alcohol

Answer 15

• Put the alcohol (in excess) and acidified potassium dichromate in a pear shaped flask and connect it to distillation equipment.
• Heat the mixture gently and the aldehyde will start evaporating off of it as it has a lower melting point than alcohols.

Question 16

How do you prepare a carboxylic acid from an alcohol?

Answer 16

You have to use a primary alcohol and reflux it instead of distilling it. You have to use an excess of the oxidising agent to make sure all of the alcohol is oxidised and that any aldehyde formed is also oxidised.

Question 17

Describe the process of making a carboxylic acid from an alcohol

Answer 17

• Put the alcohol and an excess of acidified potassium dichromate into a round bottomed flask with anti-bumping granules to make the boiling smoother.
• Heat the mixture and it will oxidise vigorously and evaporate and condense back into the flask until a carboxylic acid is formed.

Question 18

How do you prepare a ketone from an alcohol?

Answer 18

You have to oxidise a secondary alcohol under reflux using potassium dichromate acidified solution until it forms a ketone.

Question 19

How do you oxidise a tertiary alcohol?

Answer 19

A tertiary alcohol cannot be oxidised so the dichromate solution remains orange when added to a tertiary alcohol. This is because tertiary alcohols have no adjacent hydrogens on the carbons so oxidation does not occur easily

Question 20

What product is always formed when alcohols are oxidised?

Answer 20

Water

Question 21

What is the dehydration of an alcohol?

Answer 21

It is an elimination where water is removed from an alcohol under reflux to produce an alkene. You need H2SO4 as a catalyst.

Question 22

What is a substitution reaction for alcohols?

Answer 22

Alcohols can react with halogens to form haloalkanes in a substitution reaction. The alcohol is heated under reflux with sulphuric acid to form a haloalkane and water.

Question 23

What is the esterification of an alcohol?

Answer 23

This is when carboxylic acid is added to an alcohol to form an ester and water. you also need a H2SO4 catalyst.

Question 24

How do you name the product of the esterification of an alcohol?

Answer 24

You name the group attached to the O group first and then you name the ester part that is attached to the double bond and add ethanoate

Question 25

Are alcohols acids or bases?

Answer 25

They are bases because they donate electron pairs

Question 26

What are nucleophiles?

Answer 26

A species that can attract electrons or is attracted to an electron-deficient centre. It also donates pairs of electrons

Question 27

Are alcohols nucleophiles and why?

Answer 27

They are because they have a lone pair of electrons on the oxygen