Lab 4 Chemical Tests

Solubility Test

• soluble in pure water - small molecules

• soluble in 5% NaHCO3 (weak base) - carboxylic acids, small molecules

• soluble in NaOH (strong base) - phenol, small molecules

• soluble in HCl (acid) - amine, small molecules

• insoluble - aldehyde, ketone, ester, alcohol

Cerium Test

goal - test for alcohols or phenols

• looking for pronounced color change (specifically red)

Ferric Test

goal - test for phenols or esters

• part 1 - tests for phenols

• part 2 - tests for esters

• looking for pronounced color change in both for positive result

*carbonyls that easily tautomerize to enols can give false positive

Tollens Test

goal - test for aldehydes

• oxidation of aldehydes to carboxylic acid, silver precipitates as solid “silver mirror”

• looking for silver mirror on glass

aldehyde + Ag(NH3)2 ——> carboxylic acid + Ag(s)

Nitrous Acid Test

goal - test for amines & type of amine

• primary alkyl amines - immediately release N2 gas, even at cold temp

• primary aryl amines - release N2 gas when warmed

• primary aryl amines can be converted to diazonium ion then azo dye (color change)

• secondary amines form yellow nitroso compound

*ketones or phenols can sometimes give a false positive

Oxime Test

goal - test for aldehydes and ketones, only done if other tests were inconclusive

• carbonyl reacts with NH2OH to form an oxime

*some easily oxidized alcohols (allylic/benzylic alcohols) can give a false positive since they oxidize to carbonyls (ketones, aldehydes, carboxylic acids)