Purifying an organic liquid

Question 1

when producing organic compounds in the lab, the product is often far from pure as it could be contaminated with

Answer 1

unreacted starting materials

other organic products

the inorganic reagents used, or the inorganic product

water

Question 2

the techniques used to separate the intended products from a reaction mixture depend on whether the intended product is a

Answer 2

gas, liquid or solid

Question 3

all of the following techniques are used to purify

Answer 3

organic liquids only

Question 4

the four techniques for separating in tended products from reaction mixtures are:

Answer 4

simple distillation
fractional distillation
solvent extraction
drying

Question 5

to prevent leakages of gas we use glassware with……..joints

Answer 5

ground-glass joints

Question 6

the eight ‘specialist’ pieces of glass apparatus used for purification are:

Answer 6

pear-shaped flask
receiver round-bottomed flask
still head
condenser
receiver adaptor
thermometer & adaptor
separating funnel
fractionating column

Question 7

simple distillation involves the distillation of

Answer 7

an impure liquid and heating it in a flask connected to a condenser

Question 8

the liquid with the lowest boiling temperature evaporates or boils

Answer 8

first and passes through the condenser for collection in the receiver separately from any other liuqid which might evaporate later

Question 9

the thermometer in simple distillation is used to

Answer 9

see if a constant temperature is present in the pear shaped flask.

Question 10

a constant temperature in simple distillation indicates that

Answer 10

one compound is distilling over

Question 11

a change in temperature after a while in simple distillation indicates that

Answer 11

a different compound is distilling over

Question 12

a rise in temperature in simple distillation indicates

Answer 12

a new compound is distilling over

Question 13

an advantage of using simple distillation is

Answer 13

that is is quick and easy to set up

Question 14

a disadvantage of simple distillation is that

Answer 14

it does not separate the liquids as well as fractional distillation

Question 15

simple distillation should only be used is

Answer 15

the difference in the boiling temperature of the liquid being purified is more than 25° C than the other liquids in the mixture

Question 16

fractional distillation uses what apparatus?

Answer 16

pear-shaped flask, condenser, fractionating column, receiver round-bottomed flask, thermometer & adaptor

Question 17

simple distillation uses what apparatus?

Answer 17

pear-shaped flask, condenser, receiver round-bottomed flask, thermometer & adaptor

Question 18

the fractionating column usually contains

Answer 18

glass beads or pieces of broken glass

Question 19

the glass beads/ broken glass in the fractionating column act as a

Answer 19

surface on which vapour leaving the column can condense and then be evaporated again as more hot vapour passes up the column

Question 20

in fractional distillation, the vapour undergoes

Answer 20

several repeated distillations as it passes up the column

Question 21

a disadvantage of fractional distillation is that

Answer 21

it takes longer than simple distillation

Question 22

an advantage of fractional distillation is that

Answer 22

it can be used when the difference in boiling temperatures is small and when there are several compounds to be separated.

Question 23

the solvent used in solvent extraction depends on two main features:

Answer 23

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

Question 24

for solvent extraction, we use………..as apparatus

Answer 24

a separating funnel

Question 25

the steps for solvent extraction are

Answer 25

placing the reaction mixture in a separating funnel and adding the solvent
place the stopper in the neck and gentle shake the contents
allow the contents to form two separate layers
remove the stopper and open the tap to drain the lower layer into a flask, then pour the upper layer into a separate flask

Question 26

in solvent extraction, the desired organic product moves from

Answer 26

the reaction mixture to the solvent

Question 27

for solvent extraction, it is better to use the solvent in

Answer 27

small portions than in a single large volume because it is more efficient

Question 28

after the desired organic product has been separated from the reaction mixture using solvent extraction, it has to be removed from the solvent through

Answer 28

simple or fractional distillation

Question 29

many organic liquids are prepared using

Answer 29

inorganic reagents in aqueous solution

Question 30

an important feature of drying agents is that

Answer 30

it does not react with the organic liquid

Question 31

a liquid organic product may partially or even completely

Answer 31

dissolve in water

Question 32

the most common drying agents are

Answer 32

anhydrous metal salts

Question 33

the commonest anhydrous metal salts used as drying agents are

Answer 33

calcium sulfate, magnesium sulfate and sodium sulfate

Question 34

anhydrous metals from………….when they come into contact with water

Answer 34

hydrated salts

Question 35

anhydrous metal salts absorb water as

Answer 35

water of crystallisation

Question 36

anhydrous calcium chloride can also be used for some organic compounds but it

Answer 36

does react with other organic compounds and is soluble in alcohols

Question 37

anhydrous calcium chloride is soluble in

Answer 37

alcohols

Question 38

the steps for drying are

Answer 38

the drying agent is added to the organic liquid and the mixture is shaken, then left for some time
more drying agent is added until it no longer turns crystalline and stays powdery
the drying agent is removed by either decantation or by filtration

Question 39

decantation is when

Answer 39

the organic liquid is poured off the solid drying agent