16.1 - Practical Techniques in Organic Chemistry

Question 1

What are 3 properties of organic reactions?

Answer 1

Slow
Volatile - low boiling points
Flammable

Question 2

Why can’t you conduct organic reactions in a beaker with a bunsen burner?

Answer 2

Their flammability means they’ll catch fire

and their volatility means they may evaporate instead

Question 3

What process do you use and how does it work?

Answer 3

Reflux
Add anti-bumping granules - makes sure there is no flash boiling

Mixture heated, continuously boils, evaporates and condenses the vapours and recycles them back in the flask - so they can react

Question 4

What Quickfit apparatus is needed for heating under reflux?

Answer 4

• Round-bottomed/pear-shaped flask
• Vertical Liebig condenser
• Rubber tubing
• Clamp
• Stand
• Electrical (hot plate) heat source, NOT BUNSEN

Question 5

Briefly describe how the process of distillation works.

Answer 5

• Works by gentle heating of the reaction mixture
• The substances evaporate in order of increasing boiling point
• Thermometer can indicate the boiling points

Question 6

What Quickfit apparatus is needed for distillation?

Answer 6

• Liebig condenser
• Clamp and stand
• Rubber tubing
• Heat source
• Screw-cap and receiver adaptor
• Still head
• Round-bottomed/pear-shaped flask
• Thermometer

Question 7

What is redistillation and why is it used?

Answer 7

It is used to purify volatile liquids

• When a product and its impurities have different boiling points, you can use redistillation to separate them.
• You perform normal distillation, and watch for a liquid to boil, (monitor the thermometer for the boiling point of your desired product), collect out other end of flask
• Once the thermometer changes from the BP of your desired product, use a different flask to collect the liquid as this is likely to be the impurity.

Question 8

What is separation used for?

Answer 8

• If product is insoluble in water, use separation to remove any impurities that dissolve in water, e.g. salts, water soluble organic compounds.

Question 9

What apparatus is used and how is separation performed?

Answer 9

Use a separation funnel, add water

• Shake the funnel and continually invert
• The organic layer is less dense than the aqueous layer and the organic layer will sit on top.
• Run out the lower aqueous layer to remove impurities.

Question 10

During separation, what happens if the organic layer has traces of unwanted water in it?

Answer 10

To remove this water, it needs to be dried by adding a drying agent

• Add an anhydrous salt (e.g. MgSO4, CaCl2) - it binds to any water and becomes a hydrated salt.
• If the drying agent becomes lumpy, add more.
  Filter out the drying agent.