Methods of purification and analysis Flashcards
What is filtration used for?
to separate an insoluble solid from a liquid
what is residue?
the insoluble solid
what is filtrate?
the liquid
what is evaporation/crystalisation used for?
to obtain the dissolved solid in a solution
what is the purpose of heating during evaporation/crystallization?
to concentrate the solution to obtain a saturated solution for crystals to form on cooling
why is heating every salt to dryness not allowed?
so that the salt will not decompose
what is the only solution allowed to heat to dryness?
NaCl solution
what are the steps to collect dry crystals formed after evaporation/crystalisation?
cool saturated solution
filter to collect the crystals formed
wash and dry the crystals
what is used in salt preparation to obtain soluble salt?
evaporation/crystalisation
what are you supposed to do if the salt formed is insoluble?
filter and wash dry
what is distillation used for?
to obtain solvent from a solution
what is fractional distillation used for?
to separate 2 or more miscibe liquids with different boiling points
what is the purpose of boiling chips?
to ensure smooth boiling
what is the purpose of the fractionating column?
to allow for more cooler surfaces for hot vapour to condense for better separation
what is the purpose of the thermometer?
(fractional distillation)
to measure the temperature of the vapour entering the condenser
what is the purpose of the condenser?
(fractional distillation)
to condense the hot vapour into liquid
what is the direction of the water flow in the condenser?
(fractional distillation)
water in from below out from the top
why must the bulb of the thermometer be placed at the entrance of the condenser?
(fractional distillation)
so that the thermometer measures only the temperature of the hot vapour entering the condenser
what does it mean when the thermometer has a constant reading?
(fractional distillation)
it is the boiling point of the vapour
how can you tell if the hot vapour entering the condenser is pure?
(fractional distillation)
when the thermometer have a constant reading
how can you tell if all of the liquids has totally boiled off and collected?
(fractional distillation)
the temperature of the thermometer will change
which liquid will be collected first?
(fractional distillation)
the one with the lowest boiling point
why cant the receiver flask cannot be enclosed?
(fractional distillation)
so that the pressure will not build up
how does fractional distillation work? (in laboratory)
heat to evaporate the different liquids
liquid with higher bp will condense on glass beads in fractionating column and drip back into round bottom flask while liquid with lower bp continue to rise to the top of the fractionating column
the vapours enter condenser, cool and condensed and is collected as distillate
how does fractional distillation work? (in industrial)
heat to evaporate different liquids
all liquids enter bottom of column and start to diffuse upwards
the heavier fractions with higher bp will cool and condense and br collected at the bottom of the column while lighter fractions with lower bp will cool and condense at the top of column
what is chromatography used for?
to separate a very small amount of substance and identify the components of the substance
why does the starting line be drawn in pencil? (chromatography)
pencil lead will not dissolve in any solvent thus not affecting the chromatogram
why cant the starting line be drawn in pen? (chromatography)
pen ink may dissolve in the solvent thus will not affect the chromatogram
why must the starting line be above the solvent level? (chromatography)
to prevent the sample placed on the starting line from dissolving into the solvent
why does the sample size be small? (chromatography)
so that the separation will not overlap each other
DO NOT REFER SPOTS ON THE CHROMATOGRAM AS “DYE” IT SHOULD BE NAMED?
spots
how to concentrate a solution?
heat to evaporate the solvent
how to dilute a solution?
add more water to the solvent
