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Practical Flashcards

(23 cards)

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1
Q

how to use a separating funnel

A
  • shake mixture and leave to settle in the separating funnel
  • open the tap to separate the layers
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2
Q

drying agents

A
  • anhydrous magnesium sulfate (MgSO4)
  • anhydrous calcium chloride (CaCl2)
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3
Q

how could you use TLC to monitor the progress of a reaction?

A
  • place spots of controls on TLC plate
  • place a spot of the reaction mixture at regular intervals alongside controls
  • compare Rf values
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4
Q

what controls would you use when measuring the progress of a reaction using TLC?

A
  • solution of reactant
  • solution of product
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5
Q

purpose of reflux

A

prevent evaporation of reactants or products OR ensure complete reaction (check with Ed)

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6
Q

how could you separate/purify an organic liquid?

A
  • separate layers with a separating funnel
  • add drying agent to the organic layer (to remove any traces of water)
  • redistill collecting product at the desired product’s boiling point (to separate any organic substances)
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7
Q

how could you separate/purify an organic solid?

A
  • completely dissolve the solid in the minimum volume of hot solvent
  • cool the solution in an ice bath (scratch bottom of beaker with stirring rod to encourage crystal growth)
  • filter under reduced pressure
  • rinse filtrate (organic solid in buchner flask) with cool solvent
  • allow the organic solid to dry
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8
Q

how would you estimate the melting/boiling point of an impure substance?

A
  • range must be greater than that of pure
  • melting/boiling point must be lower than the pure one (highest temp of impure lower than lowest temp of pure)
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9
Q

what happens to the impurities during recrystallisation?

A
  • organic solid crystallises as it is only soluble in hot solvent
  • impurities stay in solution as they are soluble in the hot and cool solvent
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10
Q

how would you choose a solvent for recrystallisation?

A
  • impurities must be more soluble in the solvent than the organic product
  • e.g. if the impurities are non-polar and the organic product is polar, use a non-polar solvent so the organic solid only dissolves at high temperatures
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11
Q

limitations of TLC

A
  • there may not be a known Rf value for some molecules
  • similar molecules may have similar Rf values
  • molecules usually shows smudges rather than clear dots
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12
Q

adsorption (in the context of TLC)

A

process by which the solid silica holds the different substances in the mixture to its surface

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13
Q

how are molecules separated in TLC?

A

relative absorptions of substances with the stationary phase

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14
Q

when is gas chromatography used?

A

separating an identifying volatile organic compounds

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15
Q

stationary phase in gas chromatography

A

high boiling liquid or solid adsorbed onto an inert solid support

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16
Q

mobile phase in gas chromatography

Study These Flashcards
A

inert carrier gas such as helium or neon

17
Q

how are compounds separated in gas chromatography?

Study These Flashcards
A
  • separated by solubility if stationary phase is liquid
  • separated by adsorption if stationary phase is solid
18
Q

how are the Rt values measured in gas chromatography?

Study These Flashcards
A
  • each compound spends a different length of time dissolved in the liquid stationary phase
  • each compound reaches the detector at different times
  • the compound retained in the column for the shortest time has the lowest retention time and is detected first (least soluble)
19
Q

retention time

Study These Flashcards
A

time taken for each component to travel through the column in gas chromatography

20
Q

how are gas chromatograms interpreted?

Study These Flashcards
A
  • retention times are used to identify compounds present by comparing them to known retention times in data books
  • peak integrations determine the concentrations of components in the sample
21
Q

how can you determine concentrations of components in gas chromatography?

Study These Flashcards
A
  • make standard solutions of known concentrations of the compound
  • gas chromatograms must be obtained for each standard solution
  • plot a calibration curve of peak area against concentration
  • use the calibration curve to measure the unknown concentration of the compound
22
Q

test for a haloalkane

Study These Flashcards
A
  • add silver nitrate and ethanol
  • warm to 50°C in a water bath
  • chloroalkane: white ppt
  • bromoalkane: cream ppt
  • iodoalkane: yellow ppt
23
Q

test for phenol

Study These Flashcards
A
  • pH indicator paper (weak acid)
  • won’t react with Na2CO3
  • mix with bromine water and it decolorises it (from orange colour)
  • undergoes electrophilic substitution reaction with bromine at room temperature

Chemistry (13 decks)

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