Required practical 10

Question 1

What is reflux

Answer 1

The continuous boiling and condensing of a reaction mixture

Question 2

What is the role of antibumping granules

Answer 2

Prevent the formation of large bubbles

Question 3

Purpose of separation funnel

Answer 3

Seperate the mixture into two layers
The aqueous layer is less dense than the organic layer

Question 4

Separating - 1

Answer 4

Put the distillate of impure product into the separation funnel

Question 5

Separating - 2

Answer 5

Wash the product

Question 6

Washing - method 1

Answer 6

Sodium hydrogencarbonate solution - shaking and releasing pressure from CO2 released
Sodium hydrogen carbonate solution removes acidic impurities by neutralisation

Question 7

Washing - method 2

Answer 7

Saturated sodium chloride solution
Helps separate the organic layer from the aqueous layer

Question 8

Separating - 3

Answer 8

Allow layers to separate in the funnel and then run and discard the aqueous layer

Question 9

Separating - 4

Answer 9

Run organic layer into clean, dry conical flask and add 3 spatulas of drying agent (anhydrous sodium sulphate)

Question 10

What should the drying agent be

Answer 10

Insoluble in the organic liquid and unreactive with the organic liquid

Question 11

Separating - 5

Answer 11

Carefully decant the liquid into the distillation flask

Question 11

Separating - 6

Answer 11

Distill to collect clear product

Question 11

Role of anhydrous calcium carbonate

Answer 11

Drying agent - soaks up remaining water

Question 12

Determining the melting point

Answer 12

Should eb sharp and close to the value in the data book

Question 13

How would we tell if impurities are present

Answer 13

The melting point will be lowered and the sample will melt over a range of values

Question 13

How can we measure the melting point

Answer 13

Using an electric melting point machine - when it starts to melt and when it finishes

Question 14

Measuring boiling point

Answer 14

Can be done in a distillation set-up

Question 15

What should remain constant when testing boiling point

Answer 15

Pressure

Question 16

Recrystallisation - 1

Answer 16

Dissolve the impure compound in a minimum volume of hot solvent

Question 17

What is an appropriate solvent

Answer 17

Will dissolve the compound and impurities when hot
Will not dissolve the compound itself when cold

Question 18

Why is the minimum volume of solvent used

Answer 18

Obtains a saturated solution and enables crystallisation on cooling

Question 19

Recrystallisation - 2

Answer 19

Filter hot solution through the filter paper quickly

Question 20

Explanation of step 2

Answer 20

Removes any insoluble impurities and heat prevents any crystals forming during the filter process

Question 21

Recrystallisation - 3

Answer 21

Cool the filtered solution by placing the beaker in the ice

Question 22

What is the use of the ice

Answer 22

Increasing the yield of crystals

Question 23

Explanation of step 3

Answer 23

Crystals will reform but soluble impurities will remain in solution form as they are present in small quantities and not a saturates solution

Question 24

Recrystallisation - 4

Answer 24

Suction filtrate with a buchner flask to separate out crystals

Question 25

Recrystallisation - 5

Answer 25

Wash the crystals with distilled water

Question 26

Explanation of step 5

Answer 26

Remove soluble impurities

Question 27

Recystallisation - step 6

Answer 27

Dry the crystals between absorbant paper

Question 28

Explanation of step 6

Answer 28

Removes excess water which would impact percentage yield

Question 29

Loss of yield during recrystallisation

Answer 29

Crystals lost when filtering or washing
Some product stays in solution
Side reactions may occur