All A-Level Chemical Tests

Potassium iodide test for Ba²⁺, Pb²⁺ and Fe²⁺

Ba²⁺: Colourless solution/no reaction

Pb²⁺: Yellow precipitate

Fe²⁺: Green solution/no reaction

Sulfuric acid test for Ba²⁺, Pb²⁺ and Fe²⁺

Ba²⁺: White precipitate

Pb²⁺: White precipitate

Fe²⁺: Green solution/no reaction

Hydrochloric acid test for Ba²⁺, Pb²⁺ and Fe²⁺

Ba²⁺: Colourless solution/no reaction

Pb²⁺: White precipitate

Fe²⁺: Green solution/no reaction

Sodium Hydroxide/Ammonia test procedure for metal ions.

Dilute NaOH solution is added - precipitate formed and effect of excess alkali are important observations. Usually give white precipitates

Repeated with aqueous ammonia solution.

Sodium Hydroxide/Ammonia test can provide evidence for/against?

Metal ions. White, gelatinous precipitate unless otherwise stated.

Aluminium, calcium, magnesium, copper(II), iron (II), iron(III), zinc, chromium(III), manganese(II), lead(II) and Barium ion.

Sodium Hydroxide test for silver, Ag⁺

Brown precipitate

Sodium Hydroxide/Ammonia test for Calcium, Ca⁺

White Precipitate with NaOH if [Ca⁺] is high enough.

No reaction with ammonia.

Sodium Hydroxide/Ammonia test for Copper(II), Cu²⁺

Blue precipitate

Redissolves in excess ammonia only (forming deep blue solution).

Sodium Hydroxide/ammonia test for Lead(II) ions, Pb²⁺

White precipitate

redissolves in excess NaOH only, to give colourless solution.

Sodium Hydroxide/Ammonia test for Iron(II), Fe²⁺

Green precipitate

Darkens in air due to oxidation

Sodium Hydroxide/Ammonia test for Iron(III), Fe³⁺

Reddish-brown precipitate

test for iron(III) ions

add a few drops of ammonium thiocyanate solution. A blood-red coloured solution is formed

Sodium Hydroxide/Ammonia test for Zinc, Zn²⁺

White precipitate- redissolves in excess to clear colourless solution

Sodium Hydroxide/Ammonia test for Manganese (II) ions, Mn²⁺

Off-white precipitate.

Rapidly turns brown and then black in air due to oxidation.

Sodium Hydroxide/Ammonia test for chromium(III) ions, Cr³⁺

grey-green precipitate forms.

Redissolves in excess NaOH giving dark-green solution.

Sodium Hydroxide/Ammonia test for Aluminium, Al³⁺

White precipitate - insoluble in ammonia, but redissolves in excess NaOH to colourless solution

Sodium Hydroxide/Ammonia test for barium ions, Ba²⁺

No hydroxide precipitate because Ba(OH)₂ is too soluble

Sodium Hydroxide/Ammonia test for Magnesium, Mg²⁺

White precipitate

Distinguishing between Iron(II) and Iron (III)

Potassium hexacyanoferrate(III) gives deep blue (Turnbull's blue) precipitate with iron(II) ions.

Potassium hexacyanoferrate(II) gives deep blue (Prussian blue) precipitate with iron(III) ions

Lithium flame test

Crimson

Sodium flame test

Orange-yellow

Potassium flame test

Lilac

Calcium flame test

Brick red

Strontium flame test

Red

Copper(II) flame test

Blue-green

Barium flame test

yellow-green

Arsenic, antimony and bismuth flame test

blue

Test for the ammonium ion, NH₄⁺

Add cold sodium hydroxide solution and test any gas with red litmus. Gentle warming helps.

Smelly ammonia gas released, red litmus paper turns blue.

Test for acids (the H₃O+ ion)

blue litmus paper turns red, and red-orange with universal indicator.

Fizzing if sodium hydrogen carbonate is added - test that it is CO₂ gas.

Test for metal carbonates

Add acid to the carbonate and CO₂ is released.

To identify the cation, try heating the metal carbonate strongly to decompose it or examine colour of resulting solution (but apart from some transition metals, most carbonates are white giving colourless solutions). Metal ion solution may also give a flame colour or hydroxide precipitate.

Copper(II) carbonate test for carbonates

Green solid initially. When acid is added, black solid residue produced alongside CO₂.

Zinc carbonate test for carbonates

White initially. When acid added, solid residue is pale yellow when hot, and white when cold. CO₂ gas produced.

test for lead(II) ion

Add potassium iodide solution. Yellow precipitate is formed.

Test for alkene or alkyne

(any non-aromatic unsaturated hydrocarbon)

Bubble bromine gas through, or add liquid to, a solution of orange-brown bromine water. Solution rapidly decolourises as a saturated bromo-compound is formed.

Saturated alkanes give no fast reaction with bromine

Distinguish alcohols, phenols and carboxylic acids

Alcohols are neutral with pH 7, but carboxylic acids and phenols are pH<7.

Phenol does not create effervescence with sodium carbonate, but a carboxylic acid does.

Testing for hydroxy group R-OH in alcohols and phenols

Warm with ethanoic acid and conc. sulphuric acid. Pour into water and stir - characteristic ester smell produced.

Alternatively, test that no acid or amine is present first. Then, In dry conditions (as water produces a false positive), mix with drops of ethanoyl chloride (forms an ester with hydroxy group) and test fumes with litmus and silver nitrate. Litmus goes red because of HCl produced and white precipitate formed with aqueous silver nitrate. A "pleasant" ester odour sometimes detected.

Similar test with phosphorus(V) chloride, but no ester smell.

Primary alcohol test

Solution remains clear with Lucas test

Distil with potassium dichromate(VI) and conc. H₂SO₄ to produce an aldehyde turning solution from orange to green. Test for aldehyde to improve validity of test, as many other oxidisable organic compounds give the same reaction.

Lucas test procedure

Shake a few drops of sample with cold zinc chloride in concentrated HCl. Used to identify types of alcohol, as a tertiary alcohol will form an insoluble tertiary halogenalkane.

Secondary alcohol test

Solution can either remain clear or slowly become cloudy during Lucas test.

Reflux with potassium dichromate and conc. H₂SO₄. Colour change from orange to green. Test to ensure that carboxylic acid is not present (as this would indicate a primary alcohol) and that is positive test using Brady's reagent.

Tertiary alcohol test

Lucas test goes cloudy very quickly as insoluble tertiary halogenalkane is formed.

Test that no aldehyde or ketone formed during oxidation

Test for phenol (hydroxy group attached directly to aromatic ring)

Add a few drops of iron(III) chloride solution to a little of the phenol in water. Positive if gives a purple colour.

Test for carboxylic acids

mix acid with water and sodium hydrogencarbonate - fizzing produces CO₂ gas.

test for salts of aliphatic carboxylic acids

Solid/solution has no strong odour, but after adding dilute hydrochloric acid (or other mineral acid) which displaces the aliphatic carboxylic acid, a pungent odour of the original aliphatic acid is produced.

eg: ethanoic acid has smell of vinegar, and butanoates release rancid odour.

(aromatic carboxylic salts give little odour, but potentially white crystalline precipitates)

Test for Acid or Acyl Chloride

Add a few drops to water, and test with litmus and silver nitrate solution to confirm presence of HCl. Litmus goes red and white precipitate formed.

Add ethanol and pour the mixture into water - a "pleasant" ester odour is produced.

Test for Acid Amide

boil with dilute sodium hydroxide solution - test for the ammonia evolved.

(if no heat required, probably ammonium salt)

Test for aliphatic amines

Lower members have fishy smell, and are soluble in water - red litmus turns blue and white clouds form when exposed to HCl fumes.

If a salt of an aliphatic amine, add sodium hydroxide to free the amine, then the above is observed.

If in gas form, only more fishy smell distinguishes from ammonia

Test for presence of aldehydes or ketones

Add a few drops to Brady's reagent. A yellow-orange precipitate forms with both types of carbonyl

Test to distinguish aldehydes and ketones

Positive test for aldehydes ONLY

a) Warm with Tollens' reagent (ammoniacal silver nitrate): silver mirror formed on the side of the test tube - as the silver(I) ion is reduced to metal.

b) Simmer with Fehling's or Benedict's solution (complex of Cu²⁺): brown or brick-red precipitate of copper(I) oxide formed

No reactions with ketones. Reducing sugars may give a false positive test, and aromatic aldehydes do not give a positive with a

Test for ketones

Give a positive result with Brady's reagent, but no positive result with Fehlings, Tollens or Benedicts.

Test for haloalkanes

Warm with aqueous ethanolic (to increase solubility of the immiscible haloalkane) silver nitrate solution - observe a coloured precipitate and the effect of ammonia.

Or, gently simmer with aqueous NaOH (and ethanol to increase solubility). Add dilute nitric acid followed by silver nitrate and observe precipitate and the effect of ammonia.

Test for hydrogen gas, H₂

Apply lit splint - produces a squeaky pop!

Test for carbon dioxide gas, CO₂

bubble the gas through limewater (aqueous calcium hydroxide solution) - turns cloudy as milky white precipitate of calcium carbonate is produced.

Caution: CaCO₃ redissolves in excess CO₂

Test for oxygen gas, O₂

Apply a flowing splint - reignites the flame

Test for hydrochloride gas, HCl

Damp blue litmus turns red (hydrochloric acid). Does not bleach litmus like chlorine

Apply drop of silver nitrate on end of a glass rod and observe a white precipitate form.

Test for hydrogen bromide, HBr

Damp blue litmus turns red (hydrobromic acid)

Apply drop of silver nitrate on end of a glass rod and observe a cream precipitate form.

Test for hydrogen iodide, HI

Damp blue litmus turns red (hydriodic acid)

Apply drop of silver nitrate on end of a glass rod and observe a yellow precipitate form.

Test for sulphur dioxide gas, SO₂

Expose freshly prepared potassium dichromate(VI) paper to gas - changes from orange to green as the dichromate ion is reduced to the green Cr³⁺ ion

Test for ammonia gas, NH₃

Strong pungent odour.

Damp red litmus paper turns blue - ammonia is the only common alkaline gas. Gives white clouds of fine ammonium chloride cyrstals when exposed to fumes of conc. hydrochloric acid

Test for chlorine gas, Cl₂

Damp blue litmus turns red and then is bleached white.

A drop of silver nitrate on the end of a glass rod results in a white precipitate.

Test for iodine solid

Gently heat the solid - Sublimes directly from solid to brilliant purple gas-vapour.

Test for iodine solution

Add starch solution and observe blue-black colour

Test for starch

add iodine solution and observe blue-black colour

Test for hydrogen sulphide, H₂S

Rotten egg smell.

Test with damp lead(II) ethanoate paper - turns the paper black

Test for nitrogen(IV) oxide / nitrogen dioxide

Nasty orange-brown gas.

The other common brown gas is bromine - solution of nitrogen dioxide doesn't give a cream ppt. with silver nitrate solution

Test for water, liquid H₂O

Add drops to white anhydrous copper(II) sulfate, turns blue when hydrated

Dip a piece of dry blue cobalt chloride paper into sample - turns pink

Test for carbonate ion, CO₃²⁻, or hydogencarbonate HCO₃⁻

Add dilute strong acid and observe fizzing. Test colourless gas produced is CO₂

Heat compound strongly and test for CO₂ given off.

NaHCO₃ readily decomposes, by Na₂CO₃ is thermally very stable.

Test for sulphate ions, SO₄²⁻

Add dilute HCl and drops of barium chloride/nitrate solution - produces a white dense precipitate of barium sulfate.

Or, add lead(II) nitrate solution and observe white precipitate of lead(II) sulfate.

Neither precipitate is soluble in excess hydrochloric acid.

Sulphite ion, SO₃²⁻

Add dilute hydrochloric acid, producing acrid choking sulfur dioxide. Test gas with fresh potassium dichromate(VI) paper, which turns from orange to green.

Add barium chloride/nitrate solution - white precipitate of barium sulphite is produced. This dissolves in excess hydrochloric acid to give a clear colourless solution.

Test for soluble sulfide ion, S²⁻

Add lead(II) ethanoate solution, to form a black precipitate of lead sulfide.

Test for solid sulfide ion, S²⁻

Add dilute HCl acid, releasing H₂S which has a distinctive rotten egg smell. Test with gas with damp lead(II) ethanoate paper which goes black.

Test for chloride ions, Cl⁻

If soluble, add dilute nitric acid (to prevent the precipitate of other non-halide silver salts) and silver nitrate solution. White precipitate of silver chloride formed, which darkens in light and is soluble in dilute ammonia.

Add lead(II) nitrate solution - forms a white ppt. of lead(II) chloride.

If insoluble salt, add conc. sulfuric acid and warm - test for HCl fumes.

Test for Bromide ions, Br⁻

If soluble, add dilute nitric acid (to prevent the precipitate of other non-halide silver salts) and silver nitrate solution. Cream precipitate of silver bromide formed, which is soluble in conc. ammonia only.

Add lead(II) nitrate solution - forms a white ppt. of lead(II) bromide.

If insoluble salt, add conc. sulfuric acid and warm - orange vapour of bromine, and pungent fumes of SO₂ which can also be tested for.

Test for Flouride ions, F⁻

If soluble, add dilute nitric acid (to prevent the precipitate of other non-halide silver salts) and silver nitrate solution. No precipitate forms, as AgF is soluble.

Warm with conc. sulfuric acid and hold a glass rod with a drop of water on the end in the fumes - HF gas is produced by displacement which causes etching effects on the surface of the glass rod.

Test for Iodide ions, I⁻

If soluble, add dilute nitric acid (to prevent the precipitate of other non-halide silver salts) and silver nitrate solution. Yellow precipitate of silver iodide formed, which is insoluble in conc. ammonia.

Add lead(II) nitrate solution - forms a yellow ppt. of lead(II) iodide.

If insoluble salt, add conc. sulfuric acid and warm - purple iodine vapour, and rotten egg smell from hydrogen sulphide. Or test, for H₂S.

Test for nitrate(V) ions, NO₃⁻

Boil suspected nitrate with sodium hydroxide solution and Devarda's alloy (fine aluminium power) or aluminium foil. Aluminium is reducing agent, converts NO₃⁻ into NH₃. Test for ammonia.

Add iron(II) sulfate solution, the conc. sulfuric acid - where the liquids meet a brown ring forms. "Brown ring test"

Strong heat nitrates of M²⁺ salts releases nasty brown gas of nitrogen(IV) oxide, NO₂

Nitrite(III) ion, NO₂⁻

In acid solution, decomposes to give colourless NO gas which rapidly oxidises to nasty brown fumes of NO₂.

Decolourises purple acidified potassium manganate(VII).

Liberates iodine from acidified potassium iodide solution - test for iodine.

Like nitrate(V) ions: Forms ammonia with hot Al powder and NaOH, and gives brown ring test.

test for alkaline hydroxide ion, OH⁻

If pH is above 7.

Turns litmus blue. Universal indicator dark green-violet.

Add ammonium salt - ammonia is released if strongly alkaline. Test for ammonia.

Test for Chromate(VI) ions, CrO₄²⁻

Add dilute sulphuric acid - yellow solution turns orange as dichromate(VI), Cr₂O₇²⁻, is formed

Add barium chloride/nitrate solution - yellow precipitate of barium chromate(VI) is formed.

Add lead(II) nitrate - yellow precipitate of lead(II) chromate(VI) is formed.

copper carbonate

blue-green insoluble salt

silver carbonate

yellow insoluble salt

Bromine appearance

RTP: red-brown liquid

In water: yellow/orange

In hexane: orange/red

Iodine appearance

RTP: shiny grey solid

In water: brown

In hexane: pink/violet

Chlorine appearance

RTP: yellow-green gas

In water: virtually colourless

In hexane: virtually colourless

Fluorine appearance

pale yellow gas

Rule for salts that are ALWAYS soluble

SPLANE

Sodium, potassium, lithium, ammonium, nitrates, ethanoates

Solubility of chlorides, bromides, iodides

Most Soluble.

Insoluble:

silver

Lead(II) chloride and bromide - white

Lead iodide - yellow

copper iodide - white

Solubility of sulfates

Most soluble.

Insoluble:

Barium, lead(II), calcium - white

Solubility of hydroxides

Most insoluble

Soluble:

SPLANE, strontium, calcium, barium

Solubility of carbonates

Soluble: SPLANE

Insoluble:

Copper - blue/green

silver - yellow

iron(II) - white

Most others are white as well