By investigating two types of distillation methods, simple and fractional, you will be able to deduce the identities of unknown liquids in solutions and mixtures by comparing their measured boiling points with those from reference data.
Definitions
Keyword
Definition
Simple distillation
Separation of a liquid from a solution.
Fractional distillation
Separation of a liquid from a mixture.
Experiment 1: Investigating how a liquid can be separated from a solution using simple distillation
Equipment list
The following equipment is standard for following a simple distillation protocol.
EQUIPMENT
USE
10cm3 of solution
To be separated
Bunsen burner
Heat source
Tripod
To support the bunsen burner
Gauze
To rest the conical flask on
Heatproof mat
To prevent damage to surfaces
Clamp and clamp stand
To hold the test tube in place
Conical flask with delivery tube, bung and thermometer
To hold to solution for separation and allow for distillation into the test tube
Test tube in ice bath
To collect and cool the distillate
Experimental variables
The independent variable is the one you change. The dependent variable is the one you measure. The control variable is the one which remains the same.
Independent
Temperatureofthecondenser.
Dependent
Rateofdistillation.
Control
Distillationapparatusandtheheatsource.
Safety precautions
The following precautions must be taken to minimise harm to you and others.
hazard
risk
safety measure
Bunsen burner
Open flame can cause skin burns
Tie hair back, remove loose clothing and stand within a safe distance from the naked flame to minimise risk of skin burns.
Glass
If broken, may cause cuts
Handle glassware with care.
Distance between the delivery tube and test tube
Suck back when heating is discontinued
Ensure the delivery tube is at least 2cm from the bottom of the collection test tube, otherwise the distillate may rise up back into the delivery tube.
Method
The following steps should be followed to obtain the desired results of the practical.
1.
Place the 10cm3 solution in the conical flask and set up apparatus as shown above.
2.
Alight the Bunsen burner to the blue flame and begin heating the solution.
3.
Once the solution starts to boil, reduce the heat so it boils more gently.
4.
The distillate will start to condense and collect in the test tube. Record the temperature from the thermometer at which the distillate is collected.
5.
Turn off the heat, allow the apparatus to cool, and safely clear up the workspace.
6.
The distillate can now be further analysed.
Note: A limitation of this protocol is that simple distillation can only be used to separate liquids with very different boiling points. If a mixture of liquids have similar boiling points, fractional distillation must be used instead.
Analysis
The temperature recorded at the initial boiling of the liquid tells you the boiling point. You can then use this piece of information to find the identity of the liquid collected by using reference data.
Conclusion
You will have been able to conclude that the solution you separated out was made of more than one pure substance, since the distillate evaporated off at a lower temperature relative to the remainder in the conical flask.
Evaluation
As you heated the solution, the liquid of lower boiling point began to evaporate. As it entered the delivery tube, it began to condense to liquid form and formed a distillate in the test tube, changing state from gas to liquid.
Experiment 2: Investigating how a mixture of liquids can be separated using fractional distillation
Equipment list
The following equipment is standard for following a fractional distillation protocol.
eQUIPMENT
usE
20cm3 of solution
To be separated
Bunsen burner
Heat source
Tripod
To support the bunsen burner
Gauze
To rest the conical flask on
Heatproof mat
To prevent damage to surfaces
Conical flask
To hold the mixture
Fractionating column with delivery tube, bung and thermometer
To allow fractions to separate at different temperatures
Several test tubes in ice bath
To collect multiple, different distillates
Safety precautions
The following precautions must be taken to minimise harm to you and others.
hAZARD
RISK
SAFETY MEASURE
Bunsen burner
Open flame can cause skin burns
Tie hair back, remove loose clothing and stand within a safe distance to minimise risk of skin burns.
Glass
If broken, may cause cuts
Handle glassware with care.
Distance between the delivery tube and the collection test tubes
Suck back when heating is discontinued
Ensure the delivery tube is at least 2cm from the bottom of the collection test tubes, otherwise the distillate may rise back into the delivery tube.
Method
The following steps should be followed to obtain the desired results of the practical.
1.
Thermometer
2.
Cool region
3.
Fractionating column
4.
Hot region
5.
Crude oil
6.
Condenser
7.
Collected fractions
1.
Place the 20cm3 mixture in the conical flask and set up the apparatus as above.
2.
Alight the Bunsen burner to a blue flame and begin heating the solution.
3.
Once the solution starts to boil, the different liquids in the mixture will have different boiling points, so they will all evaporate at different temperatures into the delivery tube.
4.
The liquid with the lowest boiling point begins to evaporate first from the fractionating column. It will condense into the delivery tube and can be collected into the first test tube. Record the temperature at which this first distillate is collected.
5.
The liquids with higher boiling points will sequentially boil and evaporate and should be collected in the second/third test tubes and so on. Record the temperatures at which each distillate is collected.
6.
Some liquids with the highest boiling points will begin to rise up the column, however since it is too cool at the top, they condense before reaching the delivery tube and run back down the fractionating column to the base.
7.
Turn off the heat, allow the apparatus to cool, and safely clear up the workspace.
8.
The distillates in the test tubes can now be further analysed.
The temperature read from the thermometer when a liquid is at the top of the fractionating column corresponds to its boiling point.
Analysis
The temperatures recorded will allow you to confirm the identity of the liquids present in the mixture by comparing to reference data.
Conclusion
You will be able to conclude the number of pure liquids that were originally in your solution.
Evaluation
As you heat the solution, the liquid of lower boiling point evaporates first and condenses to a liquid, forming the first distillate. As heating continued, liquids of higher boiling points began to evaporate and condense. This occurred until liquids were unable to be separated as their boiling point was too high to overcome the coolness at the top of the fractionating column.
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Unit 1
Reversible changes and separation methods
Unit 2
Separating mixtures
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Unit 3
Investigating distillation methods
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FAQs - Frequently Asked Questions
When you read the thermometer in distillation practicals, what does this correspond to?
The thermometer corresponds to the boiling point of that liquid.
What is fractional distillation?
Fractional distillation is the separation of a liquid from a mixture.
What is simple distillation?
Simple distillation is the separation of a liquid from a solution.
