Practical Techniques Flashcards
what is the process of heating under reflux?
- put reagents into round bottomed flask and add anti-bumping granules
- do not stopper the flask
- add a condenser vertically to the top of the flask
- heat so the reaction boils gently
- when refluxing correctly vapours formed should reach no more than halfway up the condenser
why are anti-bumping granules used?
to allow the reaction to boil gently
draw the equipment setup for heating under reflux
what is the process of purifying a liquid organic product?
- mix product with immiscible liquid and separate layers using separating funnel
- allow layers to settle and run off aqueous layer
- run organic/product layer into a clean conical flask
- remove acidic or alkaline impurities
- dry the crude product by adding an anhydrous salt
- pure product separated by distillation
how are acidic impurities removed from an organic liquid product?
add sodium hydrogen carbonate and shake well
how are alkaline impurities removed from an organic liquid product?
add a dilute acid until solution is neutral
draw the equipment setup for purifying a liquid organic product
what are the 2 ways of making a soluble salt?
reacting acid and soluble base
reacting acid and insoluble base
what is the method of making a soluble salt by reacting an acid and soluble base?
- put base into conical flask and add acid
- transfer solution to evaporating basin and heat to remove water
- once crystals appear stop heating
- leave mixture to cool + filter
- wash with distilled water + transfer residue to watch glass and heat in oven to dry
- weigh at regular intervals and stop heating once mass constant
what is the method of making a soluble salt by reacting an acid and insoluble base?
- excess insoluble base and dilute acid in beaker
- warm until solution neutral, adding more base if needed
- leave to cool
- filter off excess base and transfer filtrate to evaporating basin
- heat evaporating basin until crystals appear
- cool, filter and wash with distilled water
- transfer to watch glass and heat in oven to dry
- weigh at regular intervals until no change in mass
draw a diagram of the process of making a soluble salt by reacting acid and insoluble base
how are water-insoluble inorganic salts made?
reaction of 2 soluble salts in solution
what is the process of making a water-insoluble inorganic salt?
- add equal volumes of salt solutions in a beaker to form precipitate of the insoluble salt
- filter precipitate and wash with deionized water
- transfer to watch glass and put in oven
- weigh at regular intervals into no change in mass
what are the methods of purification?
distillation
chromatography
recrystallisation
vacuum filtration
what is distillation used for?
to separate a mixture of miscible liquids with unique boiling points
what is the process of distillation?
- put mixture into pear-shaped flask and add anti-bumping granules
- heat until it boils gently and put collecting beaker in place
- collect distilled liquid until temp of vapour is above the boiling point of the liquid being collected
- if another compound desired, repeat
draw the equipment setup for simple distillation
what is chromatography used for?
separating small quantities of organic compounds
purifying organic substances
following the progress of reactions over time
what are the 3 forms of chromatography?
paper
thin layer
gas-liquid
what are the differences between thin layer chromatography and paper chromatography?
in TLC a silica plate is used as the stationary phase
in paper chromatography, paper is used
describe the process of TLC or paper chromatography
- spot test mixture and reference samples on a pencil line 1cm from base of the paper/plate
- suspend paper/plate in a beaker containing the solvent and cover with a lid
- remove plate when solvent front near the top
- allow plate to dry
- locate spots
- match Rf values with those of known compounds
why is a pencil used in chromatography?
it will not dissolve in a solvent
why is a lid needed in chromatography and what is an example of a suitable one?
to prevent solvent evaporating
watch glass
what is used to locate spots in chromatography?
iodine
ninhydrin
under a UV lamp
what is the mobile phase in gas-liquid chromatography?
an unreactive carrier gas
what is the stationary phase in gas-liquid chromatography?
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.
draw the equipment setup for gas-liquid chromatography
describe what happens in gas-liquid chromatography
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.
what is the partition coefficient for gas-liquid chromatography?
what does the partition coefficient show?
the distribution of components between the phases
how are the compounds detected in gas-liquid chromatography?
A detector on the outlet tube detects the compounds as they come out of the tube
Each component gives a peak on a chromatogram
what are the key components of a chromatogram?
x-axis = retention time
y-axis = signal from detector
area under peak = relative amount of a compound
what is retention time?
the time a compound is held in the column
what is used to describe a substance with a high retention time in gas-liquid chromatography?
high solubility in the stationary phase
what is recrystallisation used for?
to purify solid crude organic products with small amounts of impurities
what is the method of recrystallization?
- dissolve the substance in a minimum amount of a hot solvent where it is soluble at both high and low temperatures
- filter to remove insoluble impurities
- leave filtrate to cool until crystals form - soluble impurities stay in solution
- collect crystals by vacuum filtration to remove soluble impurities
- dry crystals in an oven
what is vacuum filtration used for?
to separate a solid from a filtrate rapidly
what is the method of vacuum filtration?
what is the process of determining the melting point of an organic solid?
