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adv higher chemistry > unit 3: organic practical techniques > Flashcards

unit 3: organic practical techniques Flashcards

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1
Q

synthesis of compound techniques

A

heating under reflux, vacuum filtration

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2
Q

purification of compound techniques

A

distillation, solvent extraction, recrystallisation

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3
Q

determination of purity techniques

A

melting point analysis, mixed melting point analysis, thin layer chromatography (TLC)

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4
Q

heating under reflux

A

heats a reaction over an extended period of time without any vapours escaping

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5
Q

heating under reflux equipment

A

condenser, round bottom flask, heating mantle

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6
Q

anti bumping granules

A

used to ensure smooth boiling

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7
Q

vacuum filtration

A

separates solids and liquids and is much faster than gravity filtration

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8
Q

vacuum filtration equipment

A

buchner funnel connected to a vacuum flask with an arm at the side connected to a water pump

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9
Q

purifying

A

removes any impurities and side products formed during the synthesis

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10
Q

recrystallisation

A

involves adding product to hot solvent to dissolve it and letting the product recrystallise as it cools down, any soluble impurities will stay dissolved in the solvent

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11
Q

things to consider when choosing a solvent

A

product must be soluble in solvent at high temperature and minimally soluble at room temperature, it must not react with the products, the solubility of the impurities

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12
Q

recrystallisation technique

A

add minimal volume of hot solvent to your synthesised product, filter the hot mixture to get rid of any insoluble impurities, let the solvent slowly cool down which will crystallise the desired product, filter off the product which will remove any soluble impurities left in the solvent

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13
Q

melting point analysis

A

works out the purity of the sample by finding it’s melting point and comparing it to a known melting point value, impurities in the sample lower and broaden the melting point since they disrupt the intermolecular bonding in the crystal lattice

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14
Q

melting point range

A

the temperature range over which it starts to melt to when it finishes melting

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15
Q

mixed melting point analysis

A

mix the sample with a pure sample of what we meant to synthesis, if the melting point is at the correct value and the range is narrow, it is pure. if a different product was made the pure sample will act as an impurity and lower the melting point

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16
Q

thin layer chromatography

A

separates compounds by their polarity using a film of silica or aluminium oxide as the stationary phase, sample is spotted on the base line and a solvent carries the compound up, a developing agent of UV light visualises the spots and the Rf value is calculated

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17
Q

Rf

A

distance travelled by the sample / distance travelled by the solvent

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18
Q

if there is only 1 spot in TLC

A

there are no impurities

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19
Q

distillation

A

separates compounds by boiling point, more volatile substances with lower boiling points will pass through first. can identify compounds by comparing boiling points or purify substances by only collecting within the target boiling point, any collected outside will be impurities

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20
Q

distillation equipment

A

burner, distilling flask, thermometer, condenser, receiving flask

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21
Q

when to use solvent extraction

A

if the product is in an aqueous solution we can use a second solvent to extract it leaving behind impurities

22
Q

choosing a second solvent in solvent extraction

A

immiscible with original solvent, desired substance is more soluble in it, volatile to allow the desired product to be easily separated, unreactive with the substance

23
Q

solvent extraction

A

done in a separatory funnel. when the extraction is carried out two layers are formed in the funnel, the substance being extracted will dissolve in both solutions and equilibrium is established. the ratio of solute dissolved in both solvent is determined by K. once settled they are run off into speared containers and process is repeated

24
Q

K in solvent extraction

A

= [substance in upper]/[substance in lower]

25
Q

improving solvent extraction

A

using smaller volumes of solvent more often

26
Q

back titration is used to

A

work out the quantity of a substance in a solid with a low solubility (meaning a standard solution cannot be made), can also be carried out if the direct titration is too slow or there is no suitable indicator

27
Q

back titration

A

the substance being analysed (A) is reacted with an excess volume of a reactant of known concentration (B). the resulting mixture is titrated with a chemical that reacts with B (C). this allows us to calculate the number of moles of B in excess and therefore the number of moles of A which reacted with it

28
Q

volumetric analysis

A

uses a standard solution to determine the concentration of another solution, usually done using a titration

29
Q

concordant results

A

within 0.1cm^3 of each other

30
Q

complexometric titrations

A

formation of a complex between a metal ion and a complexing agent e.g. EDTA, they react in a 1:1 ratio

31
Q

indicator in EDTA titrations

A

murexide indicator which turns purple at the end point

32
Q

standard solution

A

a solution of accurately known concentration

33
Q

preparing a standard solution

A

by accurate dilution of an existing solution or from a primary standard

34
Q

preparing standard solution from primary standard

A

accurately weight out primary standard and dissolve in a small volume of solvent in a beaker, transfer with rinsing to volumetric flash and make up to graduation mark with solvent, stopper and invert to mix

35
Q

preparing standard solution by dilution

A

pipette required volume of standard solution into volumetric flask, make up to the graduation mark, stopper and invert to mix

36
Q

characteristics of primary standard

A

high purity, stable as a solid in air and in solution, soluble in water, reasonably high formula mass

37
Q

common primary standards

A

EDTA, silver nitrate, oxalic acid

38
Q

sodium hydroxide

A

is not a primary standard as it absorbs moisture from the air and is unstable as a solid and in solution

39
Q

if sodium hydroxide must be used in a titration

A

a solution of approximate concentration can be prepared and standardised by carrying out another titration first to find the accurate concentration of NaOH

40
Q

stoichiometry

A

the study of mole relationships involved in chemical reactions

41
Q

yield is reduced by

A

mechanical losses, purification of product, side reactions, equilibrium position

42
Q

experimental errors

A

human error (scale reading), methodology (side reactions), uncertainties (pipettes/burettes)

43
Q

classes of equipment

A

different classes have different levels of accuracy, class A glassware is more accurate than class B

44
Q

weight accurately approximately 1g

A

the mass should be around 1g but with an accurate reading

45
Q

outline how to prepare a standard solution

A

dissolve desired reactant in deionised water and transfer with rinsings, make up to the mark in a volumetric flask

46
Q

why would you test a filtrate with standard solution

A

to check the reaction is complete

47
Q

why would volumetric analysis rather than gravimetric analysis be more appropriate

A

titration can be used with lower concentrations

48
Q

desiccator

A

prevent any water from the air reacting with the chemical

49
Q

what analytical technique could be used to determine if a specific element is present in a substance

A

absorption/emission spectra

50
Q

in TLC what affects the Rf value for an individual component

A

the solvent used

51
Q

% by mass

A

mass in 100cm^3

adv higher chemistry (18 decks)

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