What's In A Medicine?

Question 1

Give the shortened structural formula for ethanal

Answer 1

CH3CHO

Question 2

Give the shortened structural formula for ethanoic anhydride

Answer 2

(CH3CO)2O

Question 3

For mass spectrometry, give the fragments for the following fragment peaks:
17
15
77
29 (2 here)
43

Answer 3

17 - OH+
15 - CH3+
77 - C6H5+
29 - C2H5+ OR COH+
43 - C3H7+

Question 4

What is the test for the presence of a primary or secondary alcohol?

Answer 4

Acidified potassium dichromate will go from orange to green

Question 5

Describe how to make a ketone from an alcohol and state the type of alcohol required

Answer 5

Secondary alcohol; BOIL under reflux with acidified potassium dichromate solution

Question 6

What two products are produced from the oxidation of a primary alcohol? State the method of production in each

Answer 6

BOIL both with acidified potassium dichromate solution
For aldehyde –> Distill immediately
For carboxylic acid –> Heat under reflux

Question 7

Describe a method for recrystalising a solid product with small amounts of both soluble and insoluble impurities

Answer 7

1 - An appropriate solvent that the solid dissolves in well when hot but poorly when cold
2 - The impure solid is dissolved in the MINIMUM amount of hot solvent to make a SATURATED solution (MINIUM HOT SOLVENT, NOT MINIMUM SOLUTE!!)
3 - Filter the solution to remove insoluble impurities
4 - Leave the filtrate to cool, which will cause pure crystals of the solid to appear. This leaves the soluble impurities behind
5 - Collect the crystals via vacuum filtration to remove the soluble impurities
6 - Wash the crystals with a small amount of cold solvent
7 - Dry the crystals in open air or in an oven

Question 8

Give the method for carrying out Thin Layer Chromatography on a sample of impure aspirin, and how to identify the presence of impurities (8)

Answer 8

• Draw a PENCIL line 1cm from the bottom of the TLC plate/paper (1)
• Dissolve the test mixture and refrence compounds in a small amount of solvent and spot them on different MARKED places on the pencil line (2)
• Stand the plate/paper in a beaker containing the chromatography solvent, making sure the pencil line is above the solvent line (3)
• Cover the beaker with a lid to create saturated atmosphere (4)
• Allow the solvent to travel up the paper/plate. Mark it with a pencil as the ‘solvent front’ (5)
• Allow the plate/paper to dry (6)
• Use iodine crystals/UV light to highlight the spots on the plate (7)
• Analyse spots at the same level to identify where impurities are present (8)
• If impurities are present, recrystalise the aspirin again and repeat the chromatograph (9)

Question 9

Give two methods that can be used to detect colourless substances during chromatography

Answer 9

• Viewing under a UV lamp
• Place the plate/paper in a beaker with iodine crystals and cover with a lid

Question 10

What two ways can you identify the substances in a mixture via chromatography?

Answer 10

• Use refrence spots and match the heights reached with the spots of the mixture
• Use Rf values from a databook

Question 11

Give the equation for oxidation of ethanol to ethanoic acid

Answer 11

C2H6O + 2[O] –> C2H4O2 + H2O

Question 12

What does the presence of impurities do to the melting point of a sample?

Answer 12

Decreases it AND it occurs over a greater range

Question 13

How many reaction products are there from the dehydration of Butan-2-ol?

Answer 13

3 - But-1ene, Z-But-2-ene and E-But-2-ene

Question 14

Considering the following molecules, can they react with Sodium Hydroxide solution and Sodium Carbonate solution?
• Phenol
• Ethanoic Acid
• Ethanol

Answer 14

• Phenol can react with Sodium Hydroxide but not Sodium Carbonate
• Ethanoic Acid can react with both
• Ethanol can react with neither