Term
| Why do you heat under reflux? |
|
Definition
-When volatile liquids are being heated
- To prevent reactants/products from escaping whilst the reaction is in process |
|
|
Term
| What are the steps when heating under reflux? |
|
Definition
- Put the reactants in a pear-shaped flask
- Add anti-bumping granules
- Attach a condenser vertically
- Heat so the reaction mixture boils gently |
|
|
Term
| Why are anti-bumping granules added when heating under reflux? |
|
Definition
| To prevent the reaction mixture from boiling and 'bumping' out of the flask |
|
|
Term
| When heating under reflux, why is a condenser attached vertically above the reaction vessel? |
|
Definition
| To ensure any escaping vapours condense and return to the reaction flask and hence no product lost. |
|
|
Term
| How do you purify an organic liquid after is has been synthesised? |
|
Definition
| Using a separating funnel |
|
|
Term
| What techniques are used for purification? |
|
Definition
Distillation
TLC
Recrystallisation
Vacuum filtration |
|
|
Term
| Which techniques are used for analysis? |
|
Definition
Determining melting point
Acid-base titration
Redox titration
Measuring a cell e.m.f.
Colorimetry
Measuring enthalpy change of combustion |
|
|
Term
| What should the solvent for recrystallisation be? |
|
Definition
| One in which the desired substance is very soluble at high temperatures and insoluble (or nearly) at low temperatures |
|
|
Term
| What are the steps involved in recrystallisation? |
|
Definition
- Choose solvent
- Dissolve in minimum amount of hot solvent
- Filter to remove insoluble impurities
- Cool and allow crystals to form
- Collect the crystals by vacuum filtration
- Dry the crystals |
|
|
