Required practical 5: Distillation of Organic products Flashcards
One aim of this experiment is to produce aldehydes from primary alcohols.
What piece of apparatus do we use for this
Fractional distillation
This allows you to separate compounds by their boiling point
It is used when the reaction doesn’t go to completion
How do we set up the equipment for the reaction of an primary / secondary alcohol to produce an aldehyde or ketone
. Add primary alcohol with equal volume of potassium dichromate that has been acidified by dilute sulphuric acid in a pear shaped flask
. Add anti bumping granules
. Set up apparatus with a still head and condenser connected to its side
. There is a layer of silicon grease smeared over the joints of the quickfix
. Add a quickfix thermometer, where the bulb is sitting where the vapours will pass into the condenser, so it isn’t touching the liquid
. Steady and constant stream of water passes through condenser in a water jacket. The water enters from the bottom of the condenser near the flask of product and a drainage pipe removes it at the top
Why are anti bumping granules used
They prevent large gas bubbles forming which can lead to violent boiling
Why is silicon grease smeared over the joints of the quickfix
To give them a better seal
And make it easier to disassemble afterwards
How does the reaction work
Warm the primary alcohol with potassium dichromate using an electric heating mantle
It will evaporate along with some water vapour in the fractionating column
But water will condense again and stay in column whilst the aldehyde will enter condensing tube
The aldehyde has a lower boiling point than the alcohol so is distilled off
Then aldehyde vapour is condensed back into a liquid through the water column
The aldehyde is then collected in a beaker
Why do we use an electric heating mantle
Because the temperature can be controlled
And because alcohol is very flammable so using a bunsen burner isn’t a good idea
What do you do if some distillate is produced below the temperature of the boiling point of aldehydes
Throw it away and place a new beaker to collect the aldehyde
What condition do you use to get a carboxylic acid from a primary alcohol
- You carry it out under reflux
This allows the mixture to react as fully as possible without the loss of any reactants, products or solvent
Describe process of getting a carboxylic acid from a primary alcohol
. Place reaction mixture into a pear shaped flask
. Add anti bumping granules
. Place flask in heating mantle or water bath
. Set up quickfit apparatus with condenser clasped vertically in place
. Grease the joints of the apparatus
. Then a steady stream of water flows through it as a water jacket: It enters at the bottom of the condenser, and draining pipe removes it
. There is an open top
. Reaction mixture boils
. Then heating stops and it returns back to room temperature
Once you have your organic liquid produced, how do you purify it
. Use separating funnel
. Use of drying agents
. Redistillation
How do you use a separating funnel
- When organic product is made, there is usually water with it
- Water will form an aqueous layer on top of the organic product layer
- you may not know which layer is the water layer and which is the organic, so keep adding water to see which layer increases in volume
- Add sodium carbonate to neutralise acid
Stopcock is like a little tap that can be opened and closed:
- Invert the funnel many times, and open the stopcock often to release pressure build up when it is turned over so liquid doesn’t flow out
- If a neutralisation reaction has occurred, open stopcock slowly to avoid losing any product
- Then allow the two layers to separate, and if the aqueous layer is below the organic layer, open stopcock to let it drain out. Could be the other way round however.
Why would you need to add sodium carbonate to the organic product
To neutralise the sulfuric acid that is present, so to remove it
What do drying agents do
- Drying agents can be used to remove traces of water
- Eg anhydrous inorganic salts that readily hydrate in the presence of water
Such as calcium or magnesium sulfate are general drying agents
Calcium chloride dries out hydrocarbons
. So add a spatula of drying agent and swirl it
.If the drying agent will clump together, and then there is still water in the organic liquid
. So keep adding drying agent until some remains a powder
. Then filter out organic product from it
How does Redistillation work
If organic liquid is obtained via distillation, there can be remains of other liquids eg those that have a similar boiling point to the organic one
. So clean, dry and set up distillation apparatus for a second one
. Do it by making a narrower boiling point range in the distillate
