Question

Any answers in depth would be very appreciated.

1. I have an organic unknown and want to know if it is an acid or a base. What are all the possible ways to find out? Clearly indicate how you’d differentiate between an amine, a carboxylic acid, and a phenol.

2. I have a compound that turns litmus red, and very slowly causes effervescence in bicarbonate, but only with vigorous mixing. I performed the ester test and it looked okay, but all I smell is a little of the alcohol I used. Explain why the effervescence I saw required vigorous stirring to even react slowly, and why I couldn’t smell the ester.

3. I think I have an unknown that is 2-hexanol. What tests would this compound have been positive in?

4. How would I use these tests to differentiate lactic acid (-hydroxypropionic acid) and pyruvic acid (hydroxypropionic acid). Include where they would both be positive and where only one would be positive.

5. Aldehydes and ketones are closely related functional groups. Where would they both be positive and where would only one be positive.

6. Alcohols and phenols are also very similar. Where would they both be positive and when would they differentiate themselves.

Answer 1

1. Suppose your having a unknown organic compound and you want which is acid or base.

Firstly you need to do the preliminary tests i.e note physical characteristics and then perform ignition test to determine whether the compound is aliphatic or aromatic.

Secondly determine boiling point or melting point.

Thirdly you need to do the solubility tests and these tests are important to tell whether compound is acidic, basic or neutral.

Suppose if your compound is soluble in dilute HCl mostly the compounds are basic such as amines and then perform confirmation test for amines.

Suppose if your compound is soluble in dilute NaOH mostly those compounds are acidic such as most acids, phenols and then perform tests for phenols.

Suppose if your compound is soluble in Nahco3 mostly those compounds are strongly acidic such as carboxylic acids and then perform tests for carboxylic acids.

And also if your compound is soluble in cold or hot water those compounds may be neutral or acidic or basic for these you need to perform litmus test.

5. Aldehydes and ketones are carbonyl compounds.

The following tests are used to identify both aldehyde and ketone.

In 2,4-dinitrophenyl hydrazine test and sodium bisulfite test both aldehyde and ketone give positive.

Test with chromic acid : aldehydes react with chromic acid gives a green to blue precipitate. Ketones don't react with chromic acid.

Test with sodium nitroprusside: ketones reacts with alkali forms an anion further it reacts with sodium nitroprusside forms a coloured complex ion. Aldehydes don't respond to this test.