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CHEM > Methods of purification and analysis > Flashcards

Methods of purification and analysis Flashcards

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1
Q

What is filtration used for?

A

to separate an insoluble solid from a liquid

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2
Q

what is residue?

A

the insoluble solid

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3
Q

what is filtrate?

A

the liquid

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4
Q

what is evaporation/crystalisation used for?

A

to obtain the dissolved solid in a solution

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5
Q

what is the purpose of heating during evaporation/crystallization?

A

to concentrate the solution to obtain a saturated solution for crystals to form on cooling

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6
Q

why is heating every salt to dryness not allowed?

A

so that the salt will not decompose

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7
Q

what is the only solution allowed to heat to dryness?

A

NaCl solution

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8
Q

what are the steps to collect dry crystals formed after evaporation/crystalisation?

A

cool saturated solution
filter to collect the crystals formed
wash and dry the crystals

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9
Q

what is used in salt preparation to obtain soluble salt?

A

evaporation/crystalisation

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10
Q

what are you supposed to do if the salt formed is insoluble?

A

filter and wash dry

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11
Q

what is distillation used for?

A

to obtain solvent from a solution

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12
Q

what is fractional distillation used for?

A

to separate 2 or more miscibe liquids with different boiling points

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13
Q

what is the purpose of boiling chips?

A

to ensure smooth boiling

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14
Q

what is the purpose of the fractionating column?

A

to allow for more cooler surfaces for hot vapour to condense for better separation

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15
Q

what is the purpose of the thermometer?
(fractional distillation)

A

to measure the temperature of the vapour entering the condenser

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16
Q

what is the purpose of the condenser?
(fractional distillation)

A

to condense the hot vapour into liquid

17
Q

what is the direction of the water flow in the condenser?
(fractional distillation)

A

water in from below out from the top

18
Q

why must the bulb of the thermometer be placed at the entrance of the condenser?
(fractional distillation)

A

so that the thermometer measures only the temperature of the hot vapour entering the condenser

19
Q

what does it mean when the thermometer has a constant reading?
(fractional distillation)

A

it is the boiling point of the vapour

20
Q

how can you tell if the hot vapour entering the condenser is pure?
(fractional distillation)

A

when the thermometer have a constant reading

21
Q

how can you tell if all of the liquids has totally boiled off and collected?
(fractional distillation)

A

the temperature of the thermometer will change

22
Q

which liquid will be collected first?
(fractional distillation)

A

the one with the lowest boiling point

23
Q

why cant the receiver flask cannot be enclosed?
(fractional distillation)

A

so that the pressure will not build up

24
Q

how does fractional distillation work? (in laboratory)

A

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

25
Q

how does fractional distillation work? (in industrial)

A

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

26
Q

what is chromatography used for?

A

to separate a very small amount of substance and identify the components of the substance

27
Q

why does the starting line be drawn in pencil? (chromatography)

A

pencil lead will not dissolve in any solvent thus not affecting the chromatogram

28
Q

why cant the starting line be drawn in pen? (chromatography)

A

pen ink may dissolve in the solvent thus will not affect the chromatogram

29
Q

why must the starting line be above the solvent level? (chromatography)

A

to prevent the sample placed on the starting line from dissolving into the solvent

30
Q

why does the sample size be small? (chromatography)

A

so that the separation will not overlap each other

31
Q

DO NOT REFER SPOTS ON THE CHROMATOGRAM AS “DYE” IT SHOULD BE NAMED?

A

spots

32
Q

how to concentrate a solution?

A

heat to evaporate the solvent

33
Q

how to dilute a solution?

A

add more water to the solvent

CHEM (9 decks)

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