Practical Techniques

Question 1

what is the process of heating under reflux?

Answer 1

1. put reagents into round bottomed flask and add anti-bumping granules
2. do not stopper the flask
3. add a condenser vertically to the top of the flask
4. heat so the reaction boils gently
5. when refluxing correctly vapours formed should reach no more than halfway up the condenser

Question 2

why are anti-bumping granules used?

Answer 2

to allow the reaction to boil gently

Question 3

draw the equipment setup for heating under reflux

Answer 3

Question 4

what is the process of purifying a liquid organic product?

Answer 4

1. mix product with immiscible liquid and separate layers using separating funnel
2. allow layers to settle and run off aqueous layer
3. run organic/product layer into a clean conical flask
4. remove acidic or alkaline impurities
5. dry the crude product by adding an anhydrous salt
6. pure product separated by distillation

Question 5

how are acidic impurities removed from an organic liquid product?

Answer 5

add sodium hydrogen carbonate and shake well

Question 6

how are alkaline impurities removed from an organic liquid product?

Answer 6

add a dilute acid until solution is neutral

Question 7

draw the equipment setup for purifying a liquid organic product

Answer 7

Question 8

what are the 2 ways of making a soluble salt?

Answer 8

reacting acid and soluble base

reacting acid and insoluble base

Question 9

what is the method of making a soluble salt by reacting an acid and soluble base?

Answer 9

1. put base into conical flask and add acid
2. transfer solution to evaporating basin and heat to remove water
3. once crystals appear stop heating
4. leave mixture to cool + filter
5. wash with distilled water + transfer residue to watch glass and heat in oven to dry
6. weigh at regular intervals and stop heating once mass constant

Question 10

what is the method of making a soluble salt by reacting an acid and insoluble base?

Answer 10

1. excess insoluble base and dilute acid in beaker
2. warm until solution neutral, adding more base if needed
3. leave to cool
4. filter off excess base and transfer filtrate to evaporating basin
5. heat evaporating basin until crystals appear
6. cool, filter and wash with distilled water
7. transfer to watch glass and heat in oven to dry
8. weigh at regular intervals until no change in mass

Question 11

draw a diagram of the process of making a soluble salt by reacting acid and insoluble base

Answer 11

Question 12

how are water-insoluble inorganic salts made?

Answer 12

reaction of 2 soluble salts in solution

Question 13

what is the process of making a water-insoluble inorganic salt?

Answer 13

1. add equal volumes of salt solutions in a beaker to form precipitate of the insoluble salt
2. filter precipitate and wash with deionized water
3. transfer to watch glass and put in oven
4. weigh at regular intervals into no change in mass

Question 14

what are the methods of purification?

Answer 14

distillation

chromatography

recrystallisation

vacuum filtration

Question 15

what is distillation used for?

Answer 15

to separate a mixture of miscible liquids with unique boiling points

Question 16

what is the process of distillation?

Answer 16

1. put mixture into pear-shaped flask and add anti-bumping granules
2. heat until it boils gently and put collecting beaker in place
3. collect distilled liquid until temp of vapour is above the boiling point of the liquid being collected
4. if another compound desired, repeat

Question 17

draw the equipment setup for simple distillation

Answer 17

Question 18

what is chromatography used for?

Answer 18

separating small quantities of organic compounds

purifying organic substances

following the progress of reactions over time

Question 19

what are the 3 forms of chromatography?

Answer 19

paper

thin layer

gas-liquid

Question 20

what are the differences between thin layer chromatography and paper chromatography?

Answer 20

in TLC a silica plate is used as the stationary phase

in paper chromatography, paper is used

Question 21

describe the process of TLC or paper chromatography

Answer 21

1. spot test mixture and reference samples on a pencil line 1cm from base of the paper/plate
2. suspend paper/plate in a beaker containing the solvent and cover with a lid
3. remove plate when solvent front near the top
4. allow plate to dry
5. locate spots
6. match R_f values with those of known compounds

Question 22

why is a pencil used in chromatography?

Answer 22

it will not dissolve in a solvent

Question 23

why is a lid needed in chromatography and what is an example of a suitable one?

Answer 23

to prevent solvent evaporating

watch glass

Question 24

what is used to locate spots in chromatography?

Answer 24

iodine

ninhydrin

under a UV lamp

Question 25

what is the mobile phase in gas-liquid chromatography?

Answer 25

an unreactive carrier gas

Question 26

what is the stationary phase in gas-liquid chromatography?

Answer 26

a liquid with a high boiling point, held on a finely divided inert porous solid it is packed into a column which is coiled inside an oven.

Question 27

draw the equipment setup for gas-liquid chromatography

Answer 27

Question 28

describe what happens in gas-liquid chromatography

Answer 28

Sample in the gas phase ⇌ Sample dissolved in the stationary phase Components of the sample that are smaller + have a greater affinity to the mobile phase will be carried through the column quicker Those which are more soluble will come out last.

Question 29

what is the partition coefficient for gas-liquid chromatography?

Answer 29

Question 30

what does the partition coefficient show?

Answer 30

the distribution of components between the phases

Question 31

how are the compounds detected in gas-liquid chromatography?

Answer 31

A detector on the outlet tube detects the compounds as they come out of the tube Each component gives a peak on a chromatogram

Question 32

what are the key components of a chromatogram?

Answer 32

x-axis = retention time y-axis = signal from detector area under peak = relative amount of a compound

Question 33

what is retention time?

Answer 33

the time a compound is held in the column

Question 34

what is used to describe a substance with a high retention time in gas-liquid chromatography?

Answer 34

high solubility in the stationary phase

Question 35

what is recrystallisation used for?

Answer 35

to purify solid crude organic products with small amounts of impurities

Question 36

what is the method of recrystallization?

Answer 36

1. dissolve the substance in a minimum amount of a hot solvent where it is soluble at both high and low temperatures 2. filter to remove insoluble impurities 3. leave filtrate to cool until crystals form - soluble impurities stay in solution 4. collect crystals by vacuum filtration to remove soluble impurities 5. dry crystals in an oven

Question 37

what is vacuum filtration used for?

Answer 37

to separate a solid from a filtrate rapidly

Question 38

what is the method of vacuum filtration?

Answer 38

Question 39

what is the process of determining the melting point of an organic solid?

Answer 39