RP10- Preperation And Purification Of Organic Compounds

Question 1

How can the melting point of a compound determine how pure a substance is?

Answer 1

The melting point will be sharp, and the same as what is in the data books
If the sample is impure, the melting point will be lower and will melt over a range if values

Question 2

How can you measure the melting point of a sample to test its purity?

Answer 2

Use a capillary tube that is strapped to a thermometer
Place a small amount of salt into the capillary tube
Immerse the tube in some heating oil that is in a thiele tube. ,are sure the heating oil has a higher melting point than the sample
Heat the thiele tube, and measure the temperature the the sample melts at
Compare the experimental melting point with that from the data books to determine purity

Question 3

When measuring the boiling point of a substance to determine purity using distillation, what it’s important to remember?

Answer 3

To keep a standard pressure, as pressure can affect the boiling port of substances
Make sure the thermometer is above the liquid, so it measure the temp of the saturated vapour
Many substances have the same boiling point

Question 4

Describe the process of purification and recrystallisation

Answer 4

Dissolve a the impure substance in the minimum amount of hot solvent.
Filter the hot solution using filter paper
Cool by placing the sample in an ice bath. Crystals will form
Use Buchner filter to filter and separate the crystals
Wash the crystals with distilled water
Dry with a paper towel or absorbent paper

Question 5

During purification, why is the minimum amount of hot solvent used?

Answer 5

Minimum a mount used so a saturated solution is formed
Hot solvent so the solution can cool and create crystals

Question 6

During purification, why is the solute filtered while hot?

Answer 6

To remove any insoluble impurities that did not dissolve In the hot solvent

Question 7

During recrystallisation, why is the solution left to cool in an ice bath?

Answer 7

So the largest crystals possible can form

Question 8

In recrystallisation, why are the crystals washed with distilled water?

Answer 8

To remove any soluble impurities from the crystals

Question 9

After recrystallisation, why are the crystals dried?

Answer 9

To remove any excess water, because the water can affect the percentage yield of the product

Question 10

During purification and recrystallisation, why might some of the products be lost?

Answer 10

Side reactions may occur
Some Solution may not recrystallise
Crystals may be lost when filtering or washing

Question 11

Describe the feature of a Büchner funnel

Answer 11

Büchner flask with a horizontal exit fro pressure
Filter paper
Porous plate with holes
Rubber bung