Classification Tests and Unknown Functional Groups

litmus test

for H2O soluble compounds

acidic solution turns blue litmus red

basic solution turns red litmus blue

neutral solution causes no change

wet litmus test

for H2O insoluble compounds

acidic compound turns blue litmus red

basic compound turns red litmus blue

neutral compound causes no change

NaHCO3 test

positive test shows frothing from CO2 evolution for liquid carboxylic acid, or bubbling and slow dissolving for solid carboxylic acids

2,4 DNP test +

by the formation of yellow, orange, or red precipitate of corresponding hydrazone

aldehydes and ketones

2,4 DNP test -

yellow/orange color of reagent persists

esters and alcohols

Jones oxidation test +

precipitate formation and color change to green, blue, or blue-green

primary and secondary alcohols, and aldehydes

Jones oxidation test -

persistence of reagent’s orange color, even with precipitate formation

tertiary alcohols, esters, and ketones

cerium (IV) nitrate test +

color change from yellow to orange-red

phenols and tertiary alcohols

cerium (IV) nitrate test -

no color change, remains yellow

esters, ketones, carboxylic acids, and aldehydes

Lucas test +

for water-soluble alcohols

immediate cloudiness for tertiary alcohol

cloudiness from 1 to 5 minutes for secondary alcohols

cloudiness after an hour for primary alcohols

Lucas test -

no cloudiness forms

Iodoform test +

for ketones and water-insoluble alcohols

formation of bright, canary yellow solid

2-alkanols and 2-alkanones

Iodoform test -

no bright canary yellow precipitate forms

primary or secondary alcohols, and ketones

Alkaline Iron (III) hydroxamate test +

blue-red, or magenta color

esters

iron (III) chloride test +

red, blue, green, or purple color appears

phenols

decolorization of Br2/CH2Cl2 solution +

when more than 5 drops of bromine are needed for Br2 color to persist

phenols