20A.5

Question 1

what are more separating methods

Answer 1

1. solvent extraction
2. Washing
3. Drying
4. Filtration
5. recrystallisation
6. determination of Melting temp
7. determination of boiling temp

Question 2

what is solvent extraction

Answer 2

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

Question 3

the solvent used in solvent extraction should have which features

Answer 3

1. the solvent should be immiscible (not form a mixture) with the solvent containing the desired organic product
2. The desired organic product should be much more soluble in the added solvent than in the reaction mixture

Question 4

what is the method of solvent extraction

Answer 4

place the reaction mixture in the separating funnel, then add the chosen solvent - it should then form a separate layer

2. place a stopper at the neck of the funnel and gently agitate the contents of the funnel for a short while (put ur finger on the stopped, invert it, open the tap, agitate in a circular motion, close the tap, and return the funnel to its original position)
3. allow the contents to settle to two layers
4. remove the stopper and open the tap, allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask.

Question 5

to gain more of the desired organic product in solvent extraction what should we do

Answer 5

add the solvent in portion for the same total volume since it removes more if the desired product.

Question 6

after using solvent extraction to remove the desired organic product what should we next

Answer 6

the desired organic product would be mixed with the solvent used to extract it so to get it on its own we take it through simple or fractional distillation obtaining its purest version.

Question 7

what is washing using for

Answer 7

to remove the impurities from a liquid

Question 8

why might we use NaHCO3 in washing

Answer 8

to remove any excuses acid present (this applies to everything)

Question 9

what are the features of the solvent used in washing method

Answer 9

it should be able to dissolve the solid impurities but as little as possible of the liquid being purified

Question 10

what is the method for washing

Answer 10

the impure solid will be stirred in some solvent and then the mixture if filtered, if the solid is already in a filter funnel before starting we add the solvent on top of the solid, then we take the mixture but it in a separating funnel then its shaken, then we allow the two liquid layers to separate, then allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask.

Question 11

how do we dry a organic solid

Answer 11

no specail technique is needed it just needs to be left in a warm place, or in a desiccator with a suitable drying agent

Question 12

why do we need a drying agent

Answer 12

because many of the organic liquids we use may partially or fully dissolve in water, therefore water might be an impurity that needs to be removed using a drying agent

Question 13

what is the features required from a drying agent

Answer 13

to absorb water and not react with the organic liquid

Question 14

what drying agents do we use and why

Answer 14

we usually use anhydrous salts, such as calcium chloride, magnesium sulfate, and sodium sulfate, and we use them since the from hydrated salts, so when they come into contact with the water of the organic liquid they absorb the water as water of crystallisation

Question 15

what is the method of drying

Answer 15

the drying agent is adding to the liquid organic product and then left or a while (before use the drying agent is powdery but after it absorbs the water it becomes more crystalline) after that we add the drying agent again if it remains and if it remains powdery this is an indication that the liquid is dry, then we remove the drying agent via decantation, or filtration

Question 16

what is decantation

Answer 16

pouring the organic liquid of the solid drying agent

Question 17

what is the principal behind recrystallisation

Answer 17

it is that a solid compound to dissolved in a suitable solvent that can dissolve all of or most of the impurities without dissolving the compound being purified

Question 18

what is the method of recrystallisation

Answer 18

1. add impure solid to a conical flask
2. add some of the chosen solvent and warm until the mixture nears the boiling temp
3. if there is undissolved solid, add further solvent and warm until the mixture boils again
4. continue adding further solvent and heating until all of the soluble solid has dissolved
5. if insoluble impurities are present, then hot filtration could be done using fluted filter paper in a heated funnel
6. allow the liquid to cool until crystals of the organic solid have formed
7. more crystals can be obtained by cooling the solution below room temp in an ice bath
8. the mixture is then filtered to remove soluble impurities using a Buchner funnel or Hirsch funnel
9. the crystals are washed with small amounts of ice-cold solvent and then dried in a desiccator or warm oven

Question 19

why does the impure solid in recrystallisation need to be dissolved in minimum volume

Answer 19

to make sure that the pure solid will crystallise when the solution is cooled

Question 20

why is hot filtration used in recrystallisation

Answer 20

to make sure that the pure solid does not recrystallise and this stage

Question 21

why are crystals of pure solid formed once the solution is cooled

Answer 21

because the solid if less soluble in cold solvent than in hot solvent

Question 22

why do we wash the crystals made in recrystallisation with ice-cold solvent

Answer 22

remove any soluble impurities, and to make sure that very little of the pure solid dissolves

Question 23

how do you draw the Buchner and Hirsch funnels

Answer 23

page 276

Question 24

what is filtration under reduced preasure

Answer 24

it is one that uses a vacuum pump such as Buchner and Hirsch funnel

Question 25

how do we test for the purity of an organic compound we have prepared

Answer 25

the simplest test for purity is for a solid is to measure its melting point (where a pure solid will have a sharp melting point rather than melting over a range of temps) and for a liquid is to measure its boiling point and of course comparing with known data and estimating of pure it is

Question 26

for solid impurities will

Answer 26

reduce the melting temp

Question 27

how can we determine the purity of a solid we prepared using melting temp

Answer 27

so to melt the solid we would have the solid placed in a small capillary tube attached to a bulb of a thermometer and the placed in a liquid that has a higher boiling point than the melting temp of the solid, then we record the temp the solid melts at and compare it with known data of the pure compound and estimate the pureness

Question 28

for liquids impurities increase

Answer 28

the boiling temperature

Question 29

how can we determine the purity of a liquid we prepared using boiling temp

Answer 29

boil the organic compound using simple distillation (note that the apparatus used of this depends on the volume of liquid available and and weather its toxic or flammable so simple distillation might not always work) and then measure its boiling point, and compare it with known data of the pure compound and estimate its pureness

Question 30

why isnt determination the purity of a liquid we prepared using boiling temp as accurate

Answer 30

because you might not be able to measure the BP of your organic compound accurately enough as ur thermometer might read too high or too low, so even if the BP you measured is the same as the one in the data booklet it still might be impure a bit

Question 31

what should we also keep in mind in determination the purity of a liquid we prepared using boiling temp

Answer 31

that some liquids might have the same BP.