Chemical Tests

Flame test for lithium

scarlet

Flame test for sodium

yellow

Flame test for potassium

lilac

Flame test for rubidium

red

Flame test for strontium

red

flame test for caesium

blue

flame test for calcium

brick red

flame test for barium

green

Describe tests for halide ions

Dissolve one spatula of solid salt in a test tube with distilled water.

Add 5 drops of nitric acid and swirl.

Add 5 drops of silver nitrate and swirl.

Record colour of precipitate formed.

Test for Fl-

no precipitate in nitric acid and silver nitrate

Test for Cl-

white precipitate in nitric acid and silver nitrate

Test for Br-

cream precipitate in nitric acid and silver nitrate

Test for I-

yellow precipitate in nitric acid and silver nitrate

Use ammonia to test for AgCl

precipitate dissolves in dilute ammonia to give a colourless solution

Use ammonia to test for AgBr

precipitate dissolves in concentrated ammonia to give a colourless solution

Use ammonia to test for AgI

precipitate does not dissolve.

Test for sulphate ions

Acidify the sample with dilute HCl and add a few drops of aqueous barium chloride. If a sulphate is present a white precipitate of barium sulphate forms.

Test for bromide ions using chlorine water

A sample containing Cl2 will displace Br- ions, causing the solution to become yellow. You can then add cyclohexane and shake to produce a yellow layer.

Test for carbonates

carbonates and hydrogencarbonates will both fizz and produce CO2 with dilute HCl. Then test for CO2.

Test for ammonium compounds

Add sodium hydroxide to sample and gently heat the mixture. Test if ammonia is given off by using litmus paper. Red litmus paper turns blue.

Test for alkenes

Shake with bromine water; orange will be colourised.

Test for an aldehyde with Fehling’s.

Warm with fehling’s solution, and the mixture will change from clear blue to brick red.

Test for a haloalkane

Mix with silver nitrate solution to form a precipitate.

Why is nitric acid added before silver nitrate when testing for halide ions?

to remove any ions that may interfere.

Test for silver nitrate.

Add sodium hydroxide, a brown precipitate is formed.

Test for a tertiary alcohol if you know it is an alcohol

Add acidified potassium dichromate, shake and heat. The mixture will remain orange.

Test for an alcohol.

Mix with concentrated phosphoric acid and heat to eliminate water, then test for an alkene.

Test for alcohols

Add PCl5. Steamy white fumes may be seen, this is HCl. Test if it is acidic with blue litmus paper- turns red.

Test for aldehyde using Tollen’s

Add aqueous silver nitrate to aqueous sodium hydroxide, then drip aqueous ammonia into the solution until the silver oxide precipitate dissolves.

Add to sample and place in warm water bath.