AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Elimination: Required practical 5 Distillation of a product from a reaction.
This practical isolates a product by exploiting a difference in boiling point.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 5 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This practical isolates a product by exploiting a difference in boiling point. Heat the reaction mixture in a flask containing anti-bumping granules, using a water bath or heating mantle rather than a flame because organic liquids are flammable. The thermometer bulb sits level with the side arm, where the vapour leaves, so it reads the temperature of the vapour being condensed rather than of the liquid. Cooling water enters the condenser at the lower end and leaves at the upper end so the jacket stays full. Collect only the fraction distilling over the expected boiling range. Afterwards the distillate is usually washed in a separating funnel, releasing pressure often if carbon dioxide is produced, then dried with anhydrous calcium chloride.
What earns the marks
- The thermometer bulb level with the side arm where the vapour leaves.
- Cooling water entering the condenser at the lower end and leaving at the upper end.
- Collecting only the fraction that distils over the expected boiling range.
- Naming a drying agent such as anhydrous calcium chloride and its purpose, to remove water.
- Releasing the pressure in a separating funnel when carbon dioxide is produced.
Common mistakes and how to put them right
Placing the thermometer bulb in the liquid, so it records the flask temperature rather than the vapour.
Running the condenser water in at the top, so the jacket never fills with water.
Heating a flammable organic mixture with a naked flame.
Sealing the apparatus completely, leaving no vent for expanding vapour.
Exam tips
- Learn the thermometer position and the water flow direction as the two marks almost always available.
- If sodium carbonate is used to wash out acid, explain the pressure build-up as carbon dioxide gas.
- Quote the purpose of each reagent in the work-up, not just its name.
Try the lesson
The start of the Elimination: Required practical 5 Distillation of a product from a reaction. lesson, made from checked teaching notes for this specification point.
Have a go first
In Required practical 5, a student distils the product from the reaction mixture. What is the main purpose of distilling the product?
Listen
This practical isolates a product by exploiting a difference in boiling point. Heat the reaction mixture in a flask containing anti-bumping granules, using a water bath or heating mantle rather than a flame because organic liquids are flammable. The thermometer bulb sits level with the side arm, where the vapour leaves, so it reads the temperature of the vapour being condensed rather than of the liquid. Cooling water enters the condenser at the lower end and leaves at the upper end so the jacket stays full. Collect only the fraction distilling over the expected boiling range. Afterwards the distillate is usually washed in a separating funnel, releasing pressure often if carbon dioxide is produced, then dried with anhydrous calcium chloride. A strong answer earns marks for these points. the thermometer bulb level with the side arm where the vapour leaves. cooling water entering the condenser at the lower end and leaving at the upper end. collecting only the fraction that distils over the expected boiling range. naming a drying agent such as anhydrous calcium chloride and its purpose, to remove water. Exam tip: Learn the thermometer position and the water flow direction as the two marks almost always available.
Key words
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thermometer at the side arm
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condenser water direction
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collecting a boiling range
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drying and washing the product
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See every definition
- thermometer at the side arm
- The thermometer bulb sits level with the side arm, where the vapour leaves, so it reads the temperature of the vapour being condensed rather than of the liquid.
- condenser water direction
- Cooling water enters the condenser at the lower end and leaves at the upper end so the jacket stays full.
- collecting a boiling range
- Collect only the fraction distilling over the expected boiling range.
- drying and washing the product
- The distillate is usually washed in a separating funnel, releasing pressure often if carbon dioxide is produced, then dried with anhydrous calcium chloride.
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