PAPER 2 2020

Question 1

State the expected observation when acidified potassium dichromate (VI) reacts with alcohols

Answer 1

Orange solution turns green

Question 2

Describe 2 important precautions to take when heating the mixture of ethanol and crude aspirin during recrystallisation

Answer 2

• use water Bath instead of Bunsen burner
• heat to below boiling point

Question 3

A compound is usually mixed with Si(CH3)4 and either CCl4 or CDCl3 before recording the compounds H NMR spectrum.

State why Si(CH3)4, CCl4 and CDCl3 are used in H NMR spectroscopy.

Explain how their properties make them suitable for use in NMR spectroscopy.

Answer 3

CDCl3 or CCl4 as solvent
- Both have no H atoms so give no signals in spectrum
- CCl4 non-polar (so good solvent for non-polar organic molecules)
- CDCl3 polar covalent molecule (so good solvent for non-polar organic molecules)

TMS as reference
- Single environment
- Signal in an area away from other typical H signals
- easy to move / volatile / low BP

Inert

Question 4

Suggest why an expression for K can be written without the concentration of water

Answer 4

Water concentration is constant

Question 5

Name the type of compound shown by the formula RCOOK

Give one use for this type of compound

Answer 5

TYPE OF COMPOUND = Carboxylate salt

USE = Soap

Question 6

Type of catalyst used in cracking

Answer 6

Zeolite

Question 7

Cyclopentane molecular formula

Answer 7

C5H10

Question 8

Give a reason why carbon dioxide absorbs infrared radiation

Answer 8

C=O bonds vibrate at same frequency as IR

Question 9

Suggest 2 reasons why the value of enthalpy of combustion from this experiment is less exothermic than the data book value

Answer 9

• heat loss to surroundings
• incomplete combustion