5.6.4Unit 5. Transition Metals and Organic Nitrogen Chemistry
Organic Techniques – Preparation — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 5 parts Lesson 41 of 43 Unit quiz
Part 1 of 5Heating Under Reflux
Slow organic reactions often need sustained heating.
Purpose
- Reflux allows a reaction mixture to boil for a long time without losing volatile reactants or products.
Condenser position
- The condenser is fitted vertically so vapour condenses and runs back into the flask.
Water flow
- Cooling water enters at the bottom and leaves at the top so the jacket stays full.
Open system
- The top of the condenser must not be sealed, otherwise pressure builds and the apparatus could burst.
| Technique | Use | Example |
|---|---|---|
| Reflux | Complete a slow reaction | Oxidising ethanol to ethanoic acid |
| Distillation | Remove a product as it forms | Collecting ethanal |
| Fractional distillation | Separate liquids with close boiling points | Separating a mixture of alcohols |
Part 2 of 5Safe Heating
1
Flammable organic liquids must never be heated with a naked flame, so use an electric heater, water bath or heating mantle.
2
Add a few anti-bumping granules before heating so the liquid boils smoothly instead of erupting.
3
Fit the apparatus with a clamp on the neck of the flask and check that all joints are secure.
4
Switch on the cooling water before heating starts and keep it running until the apparatus has cooled.
5
Wear eye protection and work in a fume cupboard when the reagents or products are volatile or toxic.
Part 3 of 5Distillation to Collect a Product
Distillation to Collect a Product
Set-up
- The condenser is placed at a downward angle, so condensed liquid runs into a receiving flask.
Thermometer
- The bulb sits at the side arm so it records the temperature of the vapour that is condensing.
Aldehydes
- Oxidising a primary alcohol and distilling at once removes the aldehyde before it oxidises further.
Boiling point control
- Collecting only the fraction near the expected boiling point separates the product from other liquids.
Part 4 of 5Planning a Preparation
Choose method
- Decide whether the product needs reflux, distillation or both, depending on volatility and reaction rate.
Select quantities
- Work out reacting masses from the balanced equation and use a slight excess of a cheap reagent when appropriate.
Monitor progress
- Taking a small sample for thin-layer chromatography shows when the starting material has gone.
Record yield
- Weigh the pure product and compare it with the theoretical amount to find percentage yield.
Part 5 of 5Exam Checklist & Tips
5.6.4 – Key Points for the Exam
- Reflux Continuous boiling and condensing of a mixture so nothing is lost.
- Distillation Separation of liquids by boiling and condensing one component.
- Anti-bumping granules Small pieces added to a flask to give smooth boiling.
- Condenser A water-cooled tube that turns vapour back into liquid.
Common Mistakes
- Sealing the top of a condenser so the system is closed and could explode.
- Connecting the water the wrong way round so the jacket does not fill.
- Heating a flammable liquid with a Bunsen burner.
- Placing the thermometer bulb in the liquid rather than at the side arm during distillation.
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