synthesis

Question 1

Hazard

Answer 1

• Something which can cause harm
• i.e concentrated acids can cause severe burns

Question 2

Risk

Answer 2

• 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

Question 3

Preparing an organic liquid in 5 steps

Answer 3

SYTHESISING:
1. heat under reflux
2. distillation

PURIFYING:
3. Separating funnel
4. drying agents
5. redistillation

Question 4

The type of apparatus used when preparing an organic liquid and name them

Answer 4

QUICK FIT APPARATUS:

• pear-shaped flask
• still head
• condenser
• screw tap adaptor
• receiver
• round-bottom flask
• separating funnel]- stopper]- two-neck
  pear-shaped flask

Question 5

1. Heating under reflux

Answer 5

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

Question 6

Heating mantle

Answer 6

• 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

Question 7

How to heat under reflux SAFELY

Answer 7

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

Question 8

2. Why is distillation used?

Answer 8

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

Question 9

Basis of separation during distillation

Answer 9

• 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

Question 10

3. Separating funnel & identifying the organic layer and aqueous layer

Answer 10

• 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

Question 11

Removing acid impurities

Answer 11

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.

Question 12

4. Drying agents

Answer 12

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.

Question 13

Examples of drying agents

Answer 13

ANHYDROUS CALCIUM CHLORIDE:
- CaCl2
- Use ~ drying hydrocarbons

ANHYDROUS CALCIUM SULFATE:
- CaSO4
- Use ~ general drying

ANHYDROUS MAGNESIUM SULFATE:
- MgSO4
- Use ~ General drying

Question 14

5. Redistillation

Answer 14

• 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.

Question 15

Separation & purification of an organic liquid (copied from mark scheme)

Answer 15

Step 1

• Add to separating funnel
• Use of bottom layer (organic)

Step 2

• Dry with an anhydrous salt e.g MgSO4 OR CaCl2

Step 3

(Re)Distil at 222 ºC