Q2 To extract clove oil from cloves by steam distillation (part 1) Flashcards
Write a brief note to explain how steam distillation is used to extract oils from plant materials
When steam is passed through the plant material, it forms a gaseous emulsion with the oil in the
plant material. This very hot emulsion is forced under pressure into a Liegbig condenser which
converts the gaseous emulsion into a liquid. The oil may then be extracted from the emulsion using
an organic solvent.
define steam distillation
steam distillation is a separation process used to isolate compounds at temperatures below their decomposition temperatures.
It is carried out by bubbling steam through the material and distilling off the immiscible liquids
define the principle of steam distillation
The principle of steam distillation is that a mixture of two immiscible liquids boil at a temperature that is below that of the boiling point of each of the individual liquids.
The hot mixture of water vapour (from the steam) and oil (from the plant) is passed through a condenser and the distillate that is collected contains a mixture of water and oil
define an emulsion
an emulsion is a dispersion of small droplets of one liquid in another liquid which it is not soluble.
Why is it not possible to distil the clove oil directly from the cloves?
If the cloves were heated directly, the heat would cause them to char and the oil would be destroyed. Steam is used as the temperature is kept slightly above 100 degrees C and at this temp the clove oil is not destroyed
Why is the product of this experiment referred to as an emulsion? Name one other common emulsion found in everyday life.
An emulsion is formed when droplets of oil are dispersed in a liquid like water. Many paints are sold
in the form of emulsions. Mayonnaise is also an emulsion of oil in water
In carrying out this experiment a long glass tube open at both ends is usually placed in the
steam generator. What is the reason for this?
The long glass tube is a safety tube and is used to ensure that there is not a build-up of pressure in
the steam generator. As the pressure increases inside the steam generator, water is pushed up the
safety tube
What is the purpose of the steam trap in the experiment?
As the name suggests, the steam trap collects or traps steam that has condensed to water. If the trap
were not present, the flask containing the cloves would quickly fill up with water from the
condensed steam.
Describe how you would isolate the clove oil from the distillate.
The clove oil can be isolated using a process called solvent extraction.
This involves adding an organic solvent to the emulsion. A suitable organic solvent is petroleum ether or dichloromethane.
The emulsion and organic solvent will be added to a separating funnel and the two liquids shaken
for a few minutes in the stoppered funnel.
The two liquids separate into layers and the water layer is discarded.
The organic solvent is allowed to evaporate leaving the oil behind in the evaporating
basin
What name is given to the main constituent of the oil found in cloves?
eugenol
Why are cloves usually picked before they flower?
They are picked before they flower because this is the stage at which they are richest in oil.
Give two uses for clove oil.
Clove oil is used for flavouring food products, in antiseptics, and in perfumes and soaps.
Why is it better to use whole cloves rather than powdered cloves in this experiment?
Powdered cloves have usually lost a lot of their oil as a result of being ground to powder.
what is another name for solvent extraction?
liquid-liquid extraction
