Separation: Sublimation and Distillation

SEPARATION OF MIXTURES

SUBLIMATION AND DISTILLATION

sIMPLE AND FRACTIONAL DISTILLATION

SECTIOn 1

SUBLIMATION

This method/principle can be used to separate a substance which sublimes from a mixture.

Iodine

Ammonium salts

Dry ice (solid carbon dioxide)

Naphthalene (moth/camphor balls)

separation by sublimation

• The principle is that the solid that sublimes (ammonium chloride) has weak forces of attraction between the molecules while the other solid has stronger forces.

• The mixture is heated in an evaporating dish covered with a filter funnel.

• The substance which sublimes will be changed into a vapour and then formed back to solid on the inside of the funnel.

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Shown below is alternative apparatus for sublimation. Refer to page 27 in CSEC Chemistry by Naresh Birju

On gentle heating the iodine will sublime and purple vapours will be seen rising. Purple crystals of iodine will form on the cool bottom surface of the watch glass. The salt will not be affected by the heat and will remain as a white solid in the beaker

SECTIOn 2

simple distillation

Simple distillation usually separates SOLID/LIQUID solutions where you mainly want to collect the liquid (but the solid can be collected as well). The priniciple of this technique is that the solute and the solvent must have a difference in boiling points greater than 25oC.. Pure water can be obtained sea water via this method

Steps in Simple distillationClick on each plus sign to view more

Simple distillation

The principle is that the two substances have widely differing boiling points i.e. greater than 25oC It is done by heating the solution in a distillation flask and collecting the vapour that boils off.The (Liebig) condenser is cooled by the flow of cold water from the tap. Note: the steam and the cold water entering the condenser do not mix with each other. The water entering the condenser from the tap flows in the opposite direction to the gas/steam that is passing through the condenser to be cooled. This is for more efficient cooling of the steam. ·

Here is another diagram of the apparatus. Notice that "water in" means water coming in from a tap by a hose. "Water out" means that water is flowing out from another hose into a sink

(On the left) Video 1 on Simple DistillationIn this video, a salt and water solution is being separated. The salt remains in the distillation flask and the pure water is collected in a beaker as the distillate. This is how we obtain distilled water

Video 2 on Simple Distillation (on the right)In this video, a mixture of water and food colouring is being separated. You can clearly see how the condenser works and the (colourless) water being collected as the distillate. This is how we obtain distilled water

ANOTHER video ON SIMPLE DISTILLATION

In some cases simple distillation (often just called distillation) can be used to separate two MISCIBLE liquids in a LIQUID/LIQUID SOLUTION. HOWEVER THE DIFFERENCE IN BOILING POINT OF THE TWO LIQUIDS MUST BE GREATER THAN 250C Example acetone (b.p. 560C and water (b.p. 1000C)

SECTIOn 3

fractional distillation

This technique is used to separate miscible liquids with close boiling points like ethanol and water. The boiling points must actually be less than 25oC

DISTILLATION video

This video illutstrates the two types of distillation: SIMPLE DISTILLATION AND FRACTIONAL DISTILLATION

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Fractional distillation

Fractional distillation is used to separate two or more miscible liquids with different boiling points less than 250C e.g ethanol b.p.780C and water b.p 1000CA fractionating column along with the condenser is used. When the mixture in the distillation flask is heated, both liquids will evaporate and rise up the flask into the fractionating column. However, they will turn back to liquid when they reach the cold beads/surface inside the fractionating column and trickle back into the flask This process of the liquids evaporating and condensing inside the column happens repeatedly.

Fractional distillation

The vapour rising up the column becomes purer in ethanol (with the lower boiling point) and the liquid consisting of mostly water (with the higher boiling point) trickles back down into the flaskWhen the thermometer reaches a steady temperature of 78oC (the boiling point of the ethanol), the ethanol vapour will pass through the condenser and be cooled back to a liquid and will be collected in a beaker as the distillate. ·The temperature will stay at 78oC until all of the ethanol is distilled over. You may choose to stop the reaction at this time as once all the ethanol has been removed, the temperature will rise again until it reaches 1000C which is the boiing point of the water. At this point steam(gaseous water) will then pass througn the condenser to be collected as well. .

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END OF THE PRESENTATION

THANKYOU!

Here are two videos showing separation using sublimation