6.2.5 - Organic synthesis Flashcards
(19 cards)
Draw the apparatus for reflux
It’s important to be able to draw and label this apparatus accurately.
• Don’t draw lines between flask and condenser.
• Don’t have top of condenser sealed
• Condenser must have outer tube for water that is sealed at top and bottom
• Condenser must have two openings for water in and out that are open
What do we use reflux for ?
Used e when we want to heat up volatile liquids for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.
Draw the apparatus for distillation
What do we use distillation for ?
To separate substances with different boiling points.
Draw the diagram for a Büchner funnel.
What do we use filtration for?
To separate liquids and solids
What is recrystallisation ?
A method used to purify an organic solid
How do we carry out recrystallisation ?
- Add just (the minimum amount) of hot solvent to allow the impure solid to dissolve. This will mean you have a saturated solution if your impure product. And as my many crystals will fall out of solution when cooled.
- Allow the solution to cool down slowly. Crystals will then begin to form.
- Filter to get your solid purified crystals. Wash with very cold solvent and then dry them off.
Why would there be a loss of yield in the recrystallisation process ?
- Crystals lost when filtering or washing
- Some product stays in solution after recrystallisation
- Other side reactions occurring
How can we detect impurities ?
By measuring the boiling and melting point
How do we measure the boiling point ?
- Set up a distillation apparatus.
- Gently heat the sample and measure the temperature at which it distills using the thermometer in the equipment.
- Then compare this boiling point against the data book value.
In terms of boiling point how do we know if our sample contains impurities ?
- If the boiling point is higher than what is recorded in the data book.
- Our sample boils over a range of temperatures.
Why might boiling point not be the most accurate method of testing for impurities ?
As several substances have the same boiling point.
How can we measure melting point ?
- Add a sample of solid product into a capillary tube and place into the heating element of the melting point apparatus.
- Slowly increase the temperature until the substance starts to melt.
- There is a range from when the should just starts to melt to when it fully melts.
- Compare the melting point against the data book values..
In terms of melting points how do we know if our substance is impure ?
- If the substance contains impurities the melting point will be lower and the temperature range the substance melts at will be larger.
What are the 3 key points of purifying an organic solid
- Filtration under reduced pressure.
- Recrystallisation
- Measurement of melting points
Name two drying agents
- Magnesium sulphate
- Calcium chloride
How is a drying agent used ?
How is a drying agent used ?
