Jacaranda 9.2 – Laboratory analysis: Tests for C=C, -OH and -COOH functional groups

Vocabulary flashcards covering key tests and functional groups (C=C, -OH, -COOH) from Jacaranda 9.2 notes.

C=C (carbon–carbon double bond)

A site of unsaturation in organic molecules; detected by tests for unsaturation such as bromine water, potassium permanganate, and iodine number.

Bromine water test

Qualitative test for unsaturation: Br2 adds across C=C causing the orange-brown solution to fade to colorless; decolorization indicates the presence of C=C.

Iodine number

Mass of iodine that reacts with 100 g of a substance; higher iodine number indicates more unsaturation and helps classify fats as saturated, monounsaturated, or polyunsaturated.

Iodine addition reaction

In the iodine number method, 1 mole of I2 reacts with 1 mole of C=C; more C=C bonds result in more iodine consumption.

Potassium permanganate test (KMnO4 test)

Acidified KMnO4 tests for double or triple bonds; purple KMnO4 is reduced (color changes to colorless); alkaline KMnO4 can produce green solution and MnO2 precipitate.

Hydroxyl group (R–OH)

Functional group found in alcohols; detected by tests such as the sodium metal (hydrogen pop) test and the Lucas test.

Sodium metal test (hydrogen pop test)

Qualitative test for hydroxyl groups: reaction with sodium produces hydrogen gas, observed as gas evolution and a pop when a flame is near the tube mouth.

Lucas test

Qualitative test using concentrated HCl and ZnCl2 to differentiate primary, secondary, and tertiary alcohols by rate of turbidity formation (cloudiness).

Oxidation test (Cr2O7^2− / MnO4−)

Oxidizes alcohols: primary → aldehyde (and possibly carboxylic acid), secondary → ketone, tertiary → no reaction; observed as color changes (orange to green with Cr2O7^2−; MnO4− changes color depending on oxidation state).

Esterification test

Alcohol plus carboxylic acid in concentrated sulfuric acid forms an ester and water; a fruity smell confirms ester formation and the presence of an alcohol or carboxyl group.

Carboxyl group (R–COOH)

Functional group in carboxylic acids; weak acid that partially ionizes in water and lowers pH; detected by pH indicators or acid-base tests.

pH test for carboxyl groups

Carboxylic acids lower the pH of solution; measuring pH with indicators or probes helps confirm presence of –COOH.

Hydrogen carbonate test

Carboxylic acids react with NaHCO3 to release CO2 gas; limewater may turn cloudy due to CaCO3 formation.

Limewater test

Test for CO2: bubbles or cloudiness indicate CO2 presence as CaCO3 forms from limewater reacting with CO2.

Primary/Secondary/Tertiary alcohols (Lucas test interpretation)

Classification of alcohols by their reaction with Lucas reagent; tertiary alcohols react rapidly to form turbidity, secondary more slowly, primary often show little or no turbidity quickly.