17.6 Flashcards
how can bromoethane be converted to ethyl propanoate give conditions reagents and the types of reactions
bromoethane -> ethanol
reflux with aqueous potassium hydroxide
hydrolysis reaction
ethanol -> ethyl propanoate
heat with propanoic acid using an acid catalyst
esterification reaction
give 4 ways you can extent the length of a carbon chain
- react a halogenoalkane with cyanide ion to form a nitrile
- addition of hydrogen cyanide to a carbonyl compound
- alkylation of benzene
- grinard reagents
what are Grignard reagents
organometallic compounds containing magnesium
how are Grignard reagents formed
halogenoalkane/haloarene heated under reflux with magnesium and a solvent of dry ether
what is the general equation for the formation of a Grignard reagent
R-Br + Mg -> R-Mg-Br
what is formed and what is the equation for the reaction of a Grignard reagent with carbon dioxide
carboxylic acid
RMgBr -> RCOOH
what is formed and what is the equation for the reaction of a Grignard reagent with methanal
primary alcohol
RMgBr -> RCH2OH
what is formed and what is the equation for the reaction of a Grignard reagent with an aldehyde (R’CHO)
secondary alcohol
RMgBr -> RR’CHOH
what is formed and what is the equation for the reaction of a Grignard reagent with a ketone (R’COR’’)
tertiary alcohol
RR’R’‘COH
when can Grignard reagent reactions be used to increase straight chain length
reaction with carbon dioxide and methanal
when can Grignard reagents be used to create branched molecules
reaction with aldehydes and ketones
define hazard
property of a substance that could cause harm to a user
what is a risk
the possible effect that a substance may cause to a user, this will depend on factors such as concentration and apparatus
what are mercury thermometers often replaced by to reduce risk
digital thermometer
how can you reduce risk of using a Bunsen burner
use a heating mantle instead
how can you reduce risk when heating volatile organic compounds
heat under reflux to stop the reaction mixture escaping from the reaction with a reflux condenser
where does the water enter and leave a reflux condenser
enters at the bottom near the reaction mixture and leaves at the top
how can you separate an impure liquid using simple distillation
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
why is the thermometer important in simple distillation
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
what are the advantages and disadvantages of using simple distillation
+/ 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)
what does steam distillation do
separates insoluble liquid from an aqueous solution
how is steam distillation carried out
- 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
what are the advantage of steam distillation
insoluble liquid is removed from the reaction mixture below its normal boiling temperature
what is the advantage of using steam distillation with phenylamine
the temperature at which the phenylamine distils is much lower than its boiling temperature so there is less chance of decomposition
why has the fractioning column got glass beads in it
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
what does immiscible mean
doesn’t form a mixture
what must the properties of the solvent be for solvent extraction
should be immiscible with the original solvent
desired product must be more soluble in it than the original solvent
describe solvent extraction
- 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
what is always the next step after solvent extraction
simple or fractional distillation
how can washing be used to get a pure solid
stir impure solid with solvent which dissolves impurities but as little substance as possible then filter out the now pure solid
how can washing be used to get a pure liquid
mix the mixture with a solvent which dissolves the impurities but not the substance then separate with solvent extraction (separating funnel)
state some common drying agents
calcium chloride
magnesium sulfate
sodium sulfate
how do drying agents work
the anhydrous metal salts form hydrated salts when they come into contact with water so absorb water as water of crystallization
what is observed when a drying agent is used
begins powdery than goes more crystalline
how do you know the organic liquid is dry when using drying agents
if more drying agent is added and remains powdery it indicated that the liquid is dry
what is the main piece of apparatus needed for filtration
Buchner funnel
summarise the steps in recrystallisation
- 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
how can you check a compound is pure
if solid - measure melting temperature
if liquid - measure boiling temperature
why is chromatography used
to separate a mixture into its individual components
to identify the components of a mixture
why must a lid be placed on the container for paper chromatography
to prevent evaporation of the solvent
what is the stationary phase in paper chromatography
the liquid or solid that does not move
what is the mobile phase in paper chromatography
the liquid that moves through the stationary phase and transports the components
if a component moves far up the paper what is its attraction to the mobile and stationary phase
strongly attracted to the mobile phase
weakly attracted to the stationary phase
if a component does not move far up the paper what is its attraction to the stationary and mobile phase
strongly attracted to the stationary phase
weakly attracted to the mobile phase
what is the stationary and mobile phase of paper chromatography
stationary - water trapped in the fibers of the chromatography paper
mobile - solvent
what is the equation for Rf value
distance travelled by solute/distance travelled by solvent
what does Rf stand for
retention factor
whats the difference between paper chromatography and thin layer chromatography
TLC uses a sheet of plastic or glass coated in silica or alumina instead of paper
what is the advantage of using column chromatography
larger quantities of material can be separated
