synthesis Flashcards
Hazard
- Something which can cause harm
- i.e concentrated acids can cause severe burns
Risk
- The CHANCE that the hazard will lead to injury
- Conc.H2SO4 is very corrosive, but we use protective measures, the risk of injury is LOW
Preparing an organic liquid in 5 steps
SYTHESISING:
1. heat under reflux
2. distillation
PURIFYING:
3. Separating funnel
4. drying agents
5. redistillation
The type of apparatus used when preparing an organic liquid and name them
QUICK FIT APPARATUS:
- pear-shaped flask
- still head
- condenser
- screw tap adaptor
- receiver
- round-bottom flask
- separating funnel]- stopper]- two-neck
pear-shaped flask
- Heating under reflux
HEAT is required:
- to overcome the activation energy
- increase the rate of reaction
- Ensures that the solvents, reactants & products, will NOT BE LOST
- Reaction takes place at at FIXED TEMPERATURE
- Water bath ( below 100 degrees) or a BUNSEN BURNER
Heating mantle
- During reflux, used if the liquid being heated is FLAMMABLE
- Ensures NO NAKED FLAMES are present
- This increases safety if there are any LEAKS or CRACKS in the apparatus
How to heat under reflux SAFELY
ANTI-BUMPING GRANULES:
- ensures mixture boils smoothly
- Prevents large bubbles which would cause the glassware to vibrate violently
STOPPER IS NOT USED:
- This will create a closed system
- Cause pressure to build up as heated air expands
- Cause apparatus to EXPLODE
- Why is distillation used?
Some organic reactions:
- Do not go to completion
- Make by-products as well as the desired
product
- At the end of the reflux process, the crude liquid or solid product may be left in the reaction flask
- Distillation is used to SEPARATE the PRODUCT from its IMPURITIES
Basis of separation during distillation
- Different liquids in the reaction mixture have DIFFERENT BOILING POINTS
- When heated, the liquid with the LOWEST boiling point boils FIRST as it it the most VOLATILE
- Separating funnel & identifying the organic layer and aqueous layer
- After distillation, TWO LAYERS form in the collection flask
- Adding WATER, will identify AQUEOUS layer as this layer will EXPAND
- SEPARATING FUNNEL is used to separate the two layers
Removing acid impurities
AQUEOUS SODIUM HYDROGENCARBONATE:
- add to separating funnel, stoppered, shaken, turned upside down
- Gas pressure is released as the aqueous carbonate and acid react to form CARBON DIOXIDE
- The sodium hydrogen carbonate layer is REMOVED and the organic layer is WASHED with water
- The ‘washed’ organic layer may appear CLOUDY as it contains small droplets of water.
- Drying agents
DRYING AGENT ~ an anhydrous inorganic salt that readily takes up water to become hydrated.
- used to remove TRACES OF WATER from the organic liquid
- Added SPATULA at a time and the flask is stoppered and swirled
- if the solid has stuck together in a lump, water is still present
- When the solid is dispersed as a fine powder, the organic product is DRY.
- The liquid is then DECANTED from the solid and will appear CLEAR if it is dry.
Examples of drying agents
ANHYDROUS CALCIUM CHLORIDE:
- CaCl2
- Use ~ drying hydrocarbons
ANHYDROUS CALCIUM SULFATE:
- CaSO4
- Use ~ general drying
ANHYDROUS MAGNESIUM SULFATE:
- MgSO4
- Use ~ General drying
- Redistillation
- The CLOSE BP of organic liquids means that the prepared sample still may contain ORGANIC IMPURITIES
- REDISTILLATION is used to obtain the pure product.
- The NARROWER the boiling range, the PURER the product.
