Purifying and Organic liquid

Question 1

what could a desired product from a reaction be contaminated with

Answer 1

• unreacted starting materials
• other organic products
• the inorganic reagents used or formed
• water

Question 2

what type of product do we need to know the separation techniques of

Answer 2

organic liquids

Question 3

what are the four techniques we need to know of

Answer 3

• simple distillation
• fractional distillation
• solvent extraction
• drying

Question 4

what is a problem that comes with handling organic compounds in experiments and separations

Answer 4

• they are flammable and sometimes toxic

- they also attack corks and bungs which increases the risk of leaks and contamination

Question 5

what is done to prevent those things from happening

Answer 5

• use a type of apparatus made mainly from glass

- which can be fitted together tightly using ground-glass joints

Question 6

what are better options in terms of safety than a bunsen burner when wanting to heat something in these experiments

Answer 6

heating mantle, hot water bath or hot oil bath

Question 7

what does simple distillation simply involve

Answer 7

heating something in a flask connected to a condenser

Question 8

how does simple distillation work

Answer 8

• the liquid with the lowest boiling temperature evaporates or boils off first
• it then passes into the condenser first
• this means that it can be collected in the receiver separately from any other liquid that evaporates later

Question 9

why do you place a thermometer in the set-up right above the reaction mixture

Answer 9

• to monitor the temperature of the vapour as it passes into the condenser
• if the temp remains steady it indicates that one compound is distilling over
• if the temp begins to rise it indicates that a different compounds is distilling over

Question 10

what are the advantages of using simple distillation over fractional distillation

Answer 10

it is easier to set up and is quicker to do

Question 11

what is a disadvantage of simple distillation

Answer 11

it doesnt separate the liquids as well as fractional distillation

Question 12

when should simple distillation be used

Answer 12

• when the boiling temp of the liquid being purified is very different from the other liquids in the mixture
• ideally a difference of 25C

Question 13

what is the only difference between how fractional distillation is set up from simple distillation

Answer 13

there is a fractionating column between the heating flask and the still head

Question 14

what is the column usually filled with and why

Answer 14

• glass beads or pieces of broken glass
• because it acts as a surface in which the vapour can condense
• theen be evaporated again as hot vapour passes up

Question 15

what is the reason why fractional distillation separates the liquids out more effectively

Answer 15

• the vapour should undergo several repeated distillations as it passes up the column
• which would provide a better separation

Question 16

when should fractional distillation be used

Answer 16

• when the difference in the boiling temperatures between the substances in the mixture is small
• and when there are several compounds to be separated from a mixture

Question 17

what does solvent extraction involve`

Answer 17

using a solvent to remove the desired product from the other substances in the reaction mixture

Question 18

what two requirements does the solvent need to meet

Answer 18

• it should be immiscible (not mix) with the solvent containing the desired product
• the desired product should be much more soluble in the solvent than in the reaction mixture

Question 19

what is the process of solvent extraction

Answer 19

• place the reaction mixture in a separating funnel and then add the chosen solvent (it should from a separate layer)
• place the stopper in the neck of the funnel and gently shake the contents of the funnel for a while
• allow the contents to settle into two layers
• remove the stopper and open the tap to allow the lower layer to drain into a flask
• pour the upper layer into a separate flask

Question 20

why is it better to add the solvent small portions rather than in a single large volume

Answer 20

• because it is more efficient

- as using more portions of solvent with the same total volume removes more of the desired product

Question 21

what then needs to be done in order to get the desired organic product on its own as it is now mixed with the solvent

Answer 21

simple distillation or fractional distillation needs to be used to separate them

Question 22

why is drying a separation technique in the first place

Answer 22

• a liquid organic product may partially or completely dissolve in water
• so water might be an impurity that needs to be removed by a drying agent

Question 23

what feature does the drying agent need to have

Answer 23

that it doesnt react with the organic liquid

Question 24

how is drying done

Answer 24

• the drying agent is added to the organic liquid and the mixture is swirled or shaken ten left for a bit
• before use the agent is powdery but after it looks more crystalline
• if a bit more is added and it remains powdery it indicates that the liquid is dry
• the drying agent is removed either by decantation or by filtration

Question 25

what is decantation

Answer 25

pouring the organic liquids off the solid drying agent

Question 26

what is the easiest way to test whether a liquid is pure

Answer 26

• measure its boiling temperature

- as impurities raise its boiling temp

Question 27

how would you practically do this with a liquid organic compound

Answer 27

• you would measure its temperature
• and compare it to the carefully measured boiling temps of the same compound that are online or in data books
• you can then make a decision about how pure it is

Question 28

why is using a thermometer quite inaccurate when it comes to measuring boiling temps and determining whether something is pure

Answer 28

• the thermometer might read too high or low
• so even if your measured temp exactly matches the one on the data book or online, you may wrongly assume that your compound is pure

Question 29

what is another thing that you need to be aware of when doing this

Answer 29

that some organic compounds have the same boiling temp

Question 30

What are drying agents usually

Answer 30

• anhydrous metal salts

- like calcium sulfate

Question 31

Why do do drying agents work

Answer 31

• they form hydrated salts when they come into contact with water
• so when they come into contact with water in an organic liquid they absorb the water as water of crystallisation