organic synthesis

Question 1

what is the role of the condenser in heating under reflux?

Answer 1

-water enters at bottom and leaves at top
-allows outer jacket to be completely filled with a constant supply of cold water
-this promotes the most efficient cooling of vapour in the condenser

Question 2

define drying agent

Answer 2

anhydrous inorganic salt that readily takes up water to become hydrated

Question 3

give an example of a drying agent?

Answer 3

MgSO4

Question 4

what drying agent is used for drying hydrocarbons?

Answer 4

CaCl2

Question 5

An organic liquid was prepared using a given reaction (e.g. a haloalkane, aldehyde, alkene). Describe the method you would use to obtain a pure sample of the organic liquid from the reaction mixture. ​

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Answer 5

(If there are acidic impurities, add neutralising agent e.g. sodium carbonate Na2CO3)​

Use a separating funnel to separate the organic (usually top) layer from the aqueous (usually bottom) layer​

Add an anhydrous salt (e.g. MgSO4) to the organic liquid to act as a drying agent and remove any remaining water. Add until the salt swirls freely and filter to remove solid salt.​

Redistil the remaining liquid and (if boiling point is known) collect the fraction at this temperature to obtain the pure, dry liquid.​

Question 6

what is the recrystalisation theory?

Answer 6

The solubility of most compounds in a given solvent rises with temperature. ​

The higher the temperature, the greater the mass of the compound which will remain dissolved in solution.

Question 7

how can u determine a solid compound is pure?

Answer 7

by its boiling point

A pure compound will melt at the expected temperature and it will have a sharp melting range of one or two degrees (from when it starts to melt to when melting is complete). ​

If a compound contains impurities, it will have a lower melting point and melt over a wider range of temperatures.​

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Question 8

An organic solid was prepared using a given reaction (e.g. aspirin, benzoic acid). Describe the method you would use to obtain a pure sample of the organic solid from the reaction mixture. ​

Answer 8

Filter off the impure solid (under reduced pressure) ​

Recrystallise the solid by dissolving in the minimum volume of hot solvent​

Allow to cool in an ice bath (the pure solid crystals recrystallise from the solution) and then filter off the pure solid (under reduced pressure)​

Wash the crystals with cold solvent and allow to dry. ​

The purity of the solid may be tested using melting point determination and / or thin layer chromatography.

Question 9

Give an example of a neutralizing agent

Answer 9

Na2CO3