Alcohols

Question 1

What is the general formula of alcohols?

Answer 1

CnH2n+1OH

Question 2

Describe the polarity in alcohols and therefore solubility in water.

Answer 2

• OH bond is polar due to difference in electronegativity
• Hydrogen bonds form between OH in alcohol and H20 as H delta + is attracted to lone pairs on oxygen
• Hence the alcohol is soluble in water (only short chain alcohols C1-C3)
• Carbon chain is non polar and as chain length of alcohols increase, non polar bond reduces number of interactions water and alcohol can have

Question 3

What is volatility?

Answer 3

ability to evaporate

Question 4

Describe volatility of alcohols compared to alkanes.

Answer 4

Alcohols have low volatility due to hydrogen bonding

• strongest IMF therefore requires lots of energy to break
• alkanes only contain london forces

Question 5

What is a primary, secondary, tertiary alcohol?

Answer 5

primary alcohol - OH bonded to carbon with one alkyl group
secondary alcohol - OH bonded to carbon with two alkyl groups
tertiary alcohol - OH bonded to carbon with three alkyl groups

Question 6

Combustion of alcohol:

What can alcohols be used for?

Answer 6

used as fuel to generate energy

Question 7

What colour flame do alcohols with and how do they burn?

Answer 7

light blue flame and they burn readily

Question 8

When an alcohol is being combusted what are the products?

Answer 8

carbon dioxide and water

Question 9

What reactions are possible for the oxidation of alcohols?

Answer 9

primary alcohol —> aldehyde —> carboxylic acid

secondary alcohol —> ketone

tertiary alcohol (cannot be oxidised by potassium dichromate)

Question 10

What are the reagents and conditions for oxidation of primary alcohol —> aldehyde —> carboxylic acid?
What colour change takes place?

Answer 10

(1) primary alcohol —> aldehyde

reagents: potassium dichromate (K2Cr2O7) and sulphuric acid (H2SO4)
conditions: needs to be distilled as aldehyde is being made (aldehyde has lower bp than alcohol)

colour change of orange to green

(2) primary alcohol —> carboxylic acid

reagents: excess of potassium dichromate (K2Cr2O7) and sulphuric acid (H2SO4)
conditions: needs to be heated under reflux (distil after the reaction finishes)

colour change of orange to green

Question 11

What is the structure of an aldehyde?

Answer 11

C-C-C=O

double bond O is attached to a carbon thats attached to one alkyl group
ends in -al

Question 12

What are the reagents and conditions for oxidation of secondary alcohol —> ketone?
What colour change takes place?

Answer 12

(1) secondary alcohol —> ketone

reagents: potassium dichromate (K2Cr2O7) and sulphuric acid (H2SO4)
conditions: heat under reflux

colour change from orange to green

Question 13

What is the structure of a ketone?

Answer 13

C
|
C=O
|
C

double bond O is attached to a carbon with two alkyl groups

Question 14

What are the reagents and conditions for oxidation of tertiary alcohol —> ?
What colour change takes place?

Answer 14

tertiary alcohols cant be oxidised with potassium dichromate

colour remains orange

Question 15

How would you write an equation for alcohols being oxidised?

Answer 15

alcohol + [O] —-> aldehyde/ carboxylic acid/ ketone

Question 16

What does the [O] stand for?

Answer 16

oxidising agent (potassium dichromate)

Question 17

What type of reaction is the dehydration of alcohols?

Answer 17

elimination reaction (removal of water molecule)

Question 18

What are the reagents and conditions of elimination by dehydration of alcohols (alcohols —> alkenes) ?
What is the overall general equation for the dehydration of alcohols?

Answer 18

reagents: concentrated phosphoric acid/ sulphuric acid
conditions: warms (under reflux), 180 degrees

alcohol —> alkene + water

Question 19

Which reaction can be used to go from a alcohol —> haloalkane ?

Answer 19

substitution reaction