Question

Qualitative Analysis of Organic Compounds: Pre lab questions (5 pts)

1. (1 point) Identify the functional groups based on color / odor

a. Dark yellow to red color indicates that the functional group could possibly be-------------

b. Fruity / Floral odor indicates that the functional group could possibly be-------------

c. Fishy odor indicates that the functional group could possibly be-------------

d. Sharp, biting odor indicates that the functional group could possibly be-------------

2. (0.5 pts) If a liquid is soluble in water, what does it mean about the molecular weight and number of carbon atoms?

3. (0.5 pts) A water-soluble compound turns pH paper red. Is it acidic or basic?

4. (0.5 pts) A compound gives off carbon dioxide gas bubbles upon treatment with 5% NaHCO3 (0.5 pts) solution. Is the compound acidic or basic?

5. (0.5 pts) would you expect an organic base to be soluble in 5% HCl solution?

6. (0.5 pts) Identify the functional group in a compound that decolorizes Bromine in Methylene Chloride solution

7. (0.5 pts) Identify the functional group in a compound that is soluble in 5% NaOH solution, but not 5% NaHCO3 solution. Explain the concept behind this reaction.

8. (0.25 pts) What compounds give positive Tollen’s test (Silver mirror test)?

9. (0.25 pts) What compounds give positive Iodoform test?

Answer 1

For the first question, answers are very subjective. There can be many answers to each sentence, hence please note that these answers may differ from your practical manual.

1.

a. Dark yellow to red color indicates that the functional group could possibly be: Nitro group.

b. Fruity / Floral odor indicates that the functional group could possibly be: Ester, ketone group.

c. Fishy odor indicates that the functional group could possibly be: Amines.

d. Sharp, biting odor indicates that the functional group could possibly be: Carboxylic acid.

2. If the liquid is soluble in water means the compound is low molecular weight and contains less number of carbons.

3. A water-soluble compound turns pH paper red: It is an acidic compound.

4. A compound gives off carbon dioxide gas bubbles upon treatment with 5% NaHCO3 solution: It is an acidic compound.

5. would you expect an organic base to be soluble in 5% HCl solution: Yes we may expect an organic base to be soluble in 5% HCl Solution.

Often organic bases are soluble in HCl solutions. As they make a good soluble hydrochloride salt with HCl.

6. Identify the functional group in a compound that decolorizes Bromine in Methylene Chloride solution: Alkene or alkyne

When bromine is reacted with unsaturated compounds then it forms an addition compound to give decolorization of bromine.

7. Identify the functional group in a compound that is soluble in 5% NaOH solution, but not 5% NaHCO3 solution.

All acidic compounds react with a strong base such as NaOH, however, all acidic compound may not react with a weak base such as NaHCO3. Particularly, carboxylic acid reacts with NaHCO3, but phenol does not react with NaHCO3. Phenol pKa is around 10, and hence it is not that strong acid as compared to the carboxylic acid.

So compound which is soluble in 5% NaOH but not in NaHCO3, is a phenolic compound.

8. Aldehydic compounds give positive Tollen’s test (Silver mirror test).

9. Aldehyde and ketone compound with an alpha methyl group gives positive Iodoform test. Such as acetone, acetaldehyde, acetophenone, etc.