Question

1.What is purpose of Sulferic Acid ?

2.Why aspirin not very soluble in water ? Explain full answer ?

3.Why aspirin is dissolved in alcohol in recrystallization step ? Explain full answer .

4.What impurity is most likely to be present in the sample of aspirin you prepared ? Explain full answer

Answer 1

1. Uses of sulphuric acid are as follows:

• In fertilizer industries.
• pharma industries
• water treatment.
• Automobile batteries
• Paper bleaching
• Sugar bleaching and many others.

2. Aspirin is only slightly soluble in water and acidic solutions because Aspirin contains polar functional groups which can form hydrogen bonds with polar water molecules. Besides this Aspirin is a monoprotic weak acid, K_a = 2.8 x 10^-4 at 25^oC, so very little of the molecular aspirin (acetylsalicylic acid) dissociates to form acetylsalicylate ions.
For the equilibrium dissociation reaction:

aspirin (acetylsalicylic acid)		acetylsalicylate ion	+	H+
			+	H+

the equilibrium position lies well to the left, favouring molecular aspirin.

3. The aspirin molecule is made up of a benzene ring, a carboxyl group, and an ester. It has both polar and non-polar components. Thus, the affinity of alcohol molecules for aspirin molecules is relatively similar to the affinity of alcohol molecules for each other. Thus, aspirin is disolves in alcohol.

4.In the synthesis of aspirin you will start with salicylic acid and acetic anhydride Note that it is the -OH group of salicylic acid that reacts with acetic anhydride to form an esterlike product. The carboxylic acid group of salicylic acid remains unchanged. Phosphoric acid will be used as a catalyst in this experiment.

The main impurity in the crystallized aspirin will be salicylic acid, which will co-precipitate with the aspirin if the procedure is done too quickly.