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Chemistry > 17.6 > Flashcards

17.6 Flashcards

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1
Q

how can bromoethane be converted to ethyl propanoate give conditions reagents and the types of reactions

A

bromoethane -> ethanol
reflux with aqueous potassium hydroxide
hydrolysis reaction
ethanol -> ethyl propanoate
heat with propanoic acid using an acid catalyst
esterification reaction

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2
Q

give 4 ways you can extent the length of a carbon chain

A
  • react a halogenoalkane with cyanide ion to form a nitrile
  • addition of hydrogen cyanide to a carbonyl compound
  • alkylation of benzene
  • grinard reagents
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3
Q

what are Grignard reagents

A

organometallic compounds containing magnesium

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4
Q

how are Grignard reagents formed

A

halogenoalkane/haloarene heated under reflux with magnesium and a solvent of dry ether

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5
Q

what is the general equation for the formation of a Grignard reagent

A

R-Br + Mg -> R-Mg-Br

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6
Q

what is formed and what is the equation for the reaction of a Grignard reagent with carbon dioxide

A

carboxylic acid
RMgBr -> RCOOH

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7
Q

what is formed and what is the equation for the reaction of a Grignard reagent with methanal

A

primary alcohol
RMgBr -> RCH2OH

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8
Q

what is formed and what is the equation for the reaction of a Grignard reagent with an aldehyde (R’CHO)

A

secondary alcohol
RMgBr -> RR’CHOH

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9
Q

what is formed and what is the equation for the reaction of a Grignard reagent with a ketone (R’COR’’)

A

tertiary alcohol
RR’R’‘COH

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10
Q

when can Grignard reagent reactions be used to increase straight chain length

A

reaction with carbon dioxide and methanal

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11
Q

when can Grignard reagents be used to create branched molecules

A

reaction with aldehydes and ketones

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12
Q

define hazard

A

property of a substance that could cause harm to a user

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13
Q

what is a risk

A

the possible effect that a substance may cause to a user, this will depend on factors such as concentration and apparatus

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14
Q

what are mercury thermometers often replaced by to reduce risk

A

digital thermometer

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15
Q

how can you reduce risk of using a Bunsen burner

A

use a heating mantle instead

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16
Q

how can you reduce risk when heating volatile organic compounds

A

heat under reflux to stop the reaction mixture escaping from the reaction with a reflux condenser

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17
Q

where does the water enter and leave a reflux condenser

A

enters at the bottom near the reaction mixture and leaves at the top

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18
Q

how can you separate an impure liquid using simple distillation

A

heat it in a flask connected to a condenser and the liquid with the lowest boiling temperature will pass into the condenser first and is collected in the receiver separately from the rest of the mixture

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19
Q

why is the thermometer important in simple distillation

A

because it monitors the temperature of the vapour, if temp remains steady it indicates 1 compound is being distilled off and when the temperature begins to rise another compound will be beginning to be distilled

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20
Q

what are the advantages and disadvantages of using simple distillation

A

+/ easier to set up
faster
-/ does not separate liquid as well as fractional distillation
can only be used if the bp of the liquids is significantly different (<25)

21
Q

what does steam distillation do

A

separates insoluble liquid from an aqueous solution

22
Q

how is steam distillation carried out

A
  • pass steam into a reaction mixture that contains an aqueous solution and a separate liquid layer
  • the top liquid evaporates and is collected in the receiver
23
Q

what are the advantage of steam distillation

A

insoluble liquid is removed from the reaction mixture below its normal boiling temperature

24
Q

what is the advantage of using steam distillation with phenylamine

A

the temperature at which the phenylamine distils is much lower than its boiling temperature so there is less chance of decomposition

25
Q

why has the fractioning column got glass beads in it

A

act as a surface on which the vapour leaving the column can condense and evaporate again so that repeated distillation occurs as it passes up the column which provides better separation

26
Q

what does immiscible mean

A

doesn’t form a mixture

27
Q

what must the properties of the solvent be for solvent extraction

A

should be immiscible with the original solvent
desired product must be more soluble in it than the original solvent

28
Q

describe solvent extraction

A
  • place reaction mixture in a separating funnel than add chosen solvent in small proportions as this is more effective
  • agitate mixture by inverting funnel multiple times
  • allow contents to separate into 2 layers
  • remove stopper and open tap to allow lower layer to drain out
  • then drain the top layer into a separate flask
29
Q

what is always the next step after solvent extraction

A

simple or fractional distillation

30
Q

how can washing be used to get a pure solid

A

stir impure solid with solvent which dissolves impurities but as little substance as possible then filter out the now pure solid

31
Q

how can washing be used to get a pure liquid

A

mix the mixture with a solvent which dissolves the impurities but not the substance then separate with solvent extraction (separating funnel)

32
Q

state some common drying agents

A

calcium chloride
magnesium sulfate
sodium sulfate

33
Q

how do drying agents work

A

the anhydrous metal salts form hydrated salts when they come into contact with water so absorb water as water of crystallization

34
Q

what is observed when a drying agent is used

A

begins powdery than goes more crystalline

35
Q

how do you know the organic liquid is dry when using drying agents

A

if more drying agent is added and remains powdery it indicated that the liquid is dry

36
Q

what is the main piece of apparatus needed for filtration

A

Buchner funnel

37
Q

summarise the steps in recrystallisation

A
  • add impure solid to conical flask
  • add chose solvent and warm to near boil
  • continue this until the solute has fully dissolved
  • if insoluble impurities are left then these must be filtered out
  • allow liquid to cool until crystals have formed
  • dry further with Buchner funnel
38
Q

how can you check a compound is pure

A

if solid - measure melting temperature
if liquid - measure boiling temperature

39
Q

why is chromatography used

A

to separate a mixture into its individual components
to identify the components of a mixture

40
Q

why must a lid be placed on the container for paper chromatography

A

to prevent evaporation of the solvent

41
Q

what is the stationary phase in paper chromatography

A

the liquid or solid that does not move

42
Q

what is the mobile phase in paper chromatography

A

the liquid that moves through the stationary phase and transports the components

43
Q

if a component moves far up the paper what is its attraction to the mobile and stationary phase

A

strongly attracted to the mobile phase
weakly attracted to the stationary phase

44
Q

if a component does not move far up the paper what is its attraction to the stationary and mobile phase

A

strongly attracted to the stationary phase
weakly attracted to the mobile phase

44
Q

what is the stationary and mobile phase of paper chromatography

A

stationary - water trapped in the fibers of the chromatography paper
mobile - solvent

45
Q

what is the equation for Rf value

A

distance travelled by solute/distance travelled by solvent

46
Q

what does Rf stand for

A

retention factor

47
Q

whats the difference between paper chromatography and thin layer chromatography

A

TLC uses a sheet of plastic or glass coated in silica or alumina instead of paper

48
Q

what is the advantage of using column chromatography

A

larger quantities of material can be separated

Chemistry (46 decks)

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