Simple distillation and fractional distillation Ena Haniff Introduction
- Slides: 20
Simple distillation and fractional distillation Ena Haniff
Introduction § If I have a solution of copper sulphate, how might we obtain the solvent? § Would evaporation be a suitable technique?
Introduction § In this lab session we are going to use a separation technique that retrieves the solvent from a solution § We are also going to separate two MISCIBLE liquids
Simple distillation The apparatus is set up as shown below
The process v The solution is heated v What happens at this point? v The vapour rises up the flask and enters the condenser v What do you think will happen to the remaining solution in the flask? v It will become more concentrated
The process v The vapour in the condenser is cooled by the flow of cold water in the outer jacket v What effect does this have on the vapour? v It causes the vapour to condense v What is the liquid that is collected in the receiving flask? v The distillate, pure water
Aim: To separate a solution and obtain the solvent v Apparatus and materials: • Thermometer, • condenser, • distillation flask, • bunsen burner, • copper sulphate solution, • retort stand, • receiving flask
Method v The apparatus was set up as shown in the diagram v Observations were noted Observations v The solution started to boil at …. . °C. v Colourless vapour evaporated and formed drops of clear liquid in the condenser. v The drops ran down the condenser and were collected in the receiving flask. v The solution in the flask became darker blue in colour v The solid eventually remained in the round bottom flask.
Simple distillation: Discussion • Simple distillation is used to separate and retain the solvent from a solution eg. To obtain water from sea water. • The method is based on the principle that the solvent is more volatile than the solute and evaporates (volatile measures the tendency to vaporise) • The solid remains in the flask and is called the residue • The distilled product is called the distillate
Simple distillation: Discussion • During the process as heat is applied, the water began to boil off and became water vapour which rose up to the top of the flask • The water vapour entered the condenser where cold water from the inlet caused the water to condense and run off into the receiving flask • As the water is removed from the solution, the solution got deeper in colour because it became more concentrated.
Simple distillation: Conclusion • The separation technique of simple distillation was effective in retrieving the solvent from a solution • The distillate obtained is water • Solution pure solvent (as vapour) pure solvent (as liquid)
Aim: To separate a mixture of miscible liquids v Apparatus and materials: • Fractionating column • Thermometer, • condenser, • 3 distillation flasks, • bunsen burner, • Solution (alcohol and water), • retort stand,
Method v The apparatus was set up as shown in the diagram v Observations were noted Observations v The solution started to boil at …. . °C. v Vapours evaporated from the solution and travelled up the fractionating column v The vapours cooled and condensed in the column v Clear, colourless drops condensed and ran down the condenser into the receiving flask where they were collected v After the first fraction was obtained, a sharp rise in temperature was noted and a second fraction was collected then v The temperature then remained at 100°C and a third fraction was collected containing a colourless liquid.
Fractional distillation: Discussion • Fractional distillation is used to separate two miscible liquids (liquids that are readily dissolved in one another) • This technique is based on the principle that one of the liquids is more volatile than the other (has a lower boiling point and vaporises first) • The boiling point of ethanol is 78° and pure water is 100°
Fractional distillation: Discussion • As the mixture of liquids was heated, the vapours rose up the fractionating column and continually condensed and vaporised, with the lower boiling point liquid (the more volatile one), rising to the higher part of the column • This liquid condensed first and was collected as the first fraction • The thermometer measures the temperature of the vapour at the top of the column and indicated what liquid is driven off
Fractional distillation: Discussion • When the temperature reaches the boiling point of the second liquid, that is then distilled into another container. • Fractional distillation is used on an industrial scale in the separation of liquid air and the refining of crude oil.
Conclusion v A mixture of miscible liquids was separated by the method of fractional distillation v The first fraction collected was alcohol and the third fraction was water v The second fraction collected a mixture of two fractions.
Applications of fractional distillation v Can you suggest an application of fractional distillation? v Separation of crude oil