Functional group tests

Describe the test and positive observation for alkenes

Test: Add bromine water

Observation: Orange → colourless

Describe the test and positive observation for primary and secondary alcohols

Test: Add acidified potassium dichromate (H⁺/Cr₂O₇^2-)

Observation: Orange → green (no change for tertiary alcohols)

Describe the tests and positive observations for aldehydes

Test 1: Warm with Tollen’s reagent

Observation 1: Silver mirror forms

Test 2: Warm with Fehling’s solution

Observation 2: Blue → brick red precipitate

Describe the test and positive observation for carboxylic acids

Test: Add Na₂CO₃

Observation: Effervescence

Describe the test and observations for determining halogenoalkanes

Test:

1. Warm with aqueous sodium hydroxide (to release halide ion)

2. Add nitric acid to prevent interference from other ions which could also form precipitates (acid reacts with these ions)

3. Add silver nitrate solution, precipitates of silver halides will be observed

Observations:

• Chloride = White precipitate of silver chloride

• Bromide = Cream precipitate of silver bromide

• Iodide = Yellow precipitate of silver iodide