GCE Chemistry Acceptable Colour Changes and Observations

Summary of acceptable colour changes, observations, and qualitative tests for GCE Chemistry AS and A2 (CCEA).

Fluorine ($F_2$)

Yellow gas

Chlorine ($Cl_2$)

Green/yellow-green/green-yellow gas

Bromine ($Br_2$)

Red-brown/brown-red liquid (and vapour)

Iodine ($I_2$) solid

Grey-black/black-grey

Iodine ($I_2$) vapour

Violet/purple

Chlorine water

Green/colourless

Bromine water

Yellow/orange/brown

Iodine ($I_2$) in polar solvents

Yellow/brown

Iodine ($I_2$) in non-polar solvents

Violet/purple

Solid chloride with concentrated sulfuric acid ($H_2SO_4$)

Steamy/misty fumes (of $HCl$)

Solid bromide with concentrated sulfuric acid ($H_2SO_4$)

Steamy/misty fumes (of $HBr$) and red-brown vapour ($Br_2$)

Solid iodide with concentrated sulfuric acid ($H_2SO_4$)

Steamy/misty fumes (of $HI$), violet/purple vapour ($I_2$), smell of rotten eggs ($H_2S$), yellow solid ($S$), and grey-black solid ($I_2$) on the sides of the test-tube

Methyl orange (adding acid to alkali)

Yellow to red

Methyl orange (adding alkali to acid)

Red to yellow

Phenolphthalein (adding acid to alkali)

Pink to colourless

Phenolphthalein (adding alkali to acid)

Colourless to pink

Hydrogen ($H_2$) gas test

Gives a ‘pop’ with a burning splint

Oxygen ($O_2$) gas test

Relights a glowing splint

Carbon dioxide ($CO_2$) gas test

Bubble through limewater; limewater turns milky

Lithium ($Li^+$) flame test

Crimson

Sodium ($Na^+$) flame test

Yellow/orange

Potassium ($K^+$) flame test

Lilac (pink through cobalt glass)

Calcium ($Ca^{2+}$) flame test

Brick red/red

Barium ($Ba^{2+}$) flame test

Green/apple green

Copper(II) ($Cu^{2+}$) flame test

Green-blue/blue-green

Sulfate ion ($SO_4^{2-}$) test

Add solution of barium chloride or barium nitrate to form a white precipitate

Silver nitrate test for Chloride ($Cl^-$)

White precipitate, soluble in dilute ammonia solution

Silver nitrate test for Bromide ($Br^-$)

Cream precipitate, soluble in concentrated ammonia solution

Silver nitrate test for Iodide ($I^-$)

Yellow precipitate, insoluble in concentrated ammonia solution

Test for iodine using starch

Solution turns blue-black/black-blue

Test for alkenes with bromine water

Aqueous layer will decolourise after shaking

Oxidation of alcohols with acidified potassium dichromate(VI) ($K_2Cr_2O_7$)

Changes from orange to green when heated; change in smell

Reaction of Magnesium ($Mg$) with oxygen

Bright white light to form a white powder

Aldehyde test with Fehling’s solution

Form a red precipitate when heated

Aldehyde test with Tollens’ reagent

Form a silver mirror when heated

Acyl chlorides with water

Steamy/misty fumes, mixture warms up

Titration of $I_2$ with $S_2O_3^{2-}$ using starch

Straw/yellow coloured until starch added; then blue-black to colourless at endpoint

Titration of $Fe^{2+}$ with $MnO_4^-$

Acidified solution changes from colourless to pink (no indicator required)

Hexaaquacopper(II) ions with concentrated $HCl$

Blue solution changes to yellow

Vanadium oxidation states: $V^{2+}$, $V^{3+}$, $VO^{2+}$, $VO_2^+$

Violet ($V^{2+}$), Green ($V^{3+}$), Blue ($VO^{2+}$), Yellow ($VO_2^+$)

Chromium(III) ($Cr^{3+}$) precipitate with $NaOH$

Green-blue precipitate soluble in excess sodium hydroxide solution

Iron(II) ($Fe^{2+}$) precipitate with $NaOH$

Green precipitate; insoluble in excess sodium hydroxide solution/ammonia solution

Iron(III) ($Fe^{3+}$) precipitate with $NaOH$

Brown precipitate; insoluble in excess sodium hydroxide solution/ammonia solution

Aspirin preparation product

White crystals