inorganic - chemical tests

how to do a flame test

what thing to put metal on

what material e.g.2 it should be made of

what to do to it before putting metal on it, why do that

what part/type of bunsen flame

• Dip the loop of an unreactive metal wire such as nichrome or platinum in concentrated acid, and then hold it in the blue flame of a Bunsen burner until there is no colour change

• This cleans the wire loop and avoids contamination

  • Two or more ions means the colours will mix, making identification erroneous

• Dip the loop into the solid sample and place it in the edge of the blue Bunsen flame. non-luminous.

potassium ion K+

lilac

chlorine gas

damp blue litmus paper turns red, then bleached white

Lithium ion Li+

red

Sodium ion Na+

Yellow flame

Calcium ion Ca 2+

Red/Orange

BRICK RED

Copper ion Cu 2+

blue/green flame test

ammonium ion NH₄+

• add NaOH (sodium hydroxide)

• heat gently

• damp red litmus paper turns blue

Copper ion Cu2+ in solution

• add NaOH

• blue precipitate

Iron (II) ion Fe²+

• add NaOH

• green precipitate

Iron (III) ion Fe³+

• add NaOH

• brown precipitate

Chloride ion Cl-

• add nitric acid

• add silver nitrate

• white precipitate

bromide ion Br-

• add nitric acid

• add silver nitrate

• cream precipitate

iodide ion I-

• add nitric acid

• add silver nitrate

• yellow precipitate

why add nitric acid to halide solution? (2)

to remove any carbonate ions because AgCO3 is also a white precipitate - would confuse results

CO3²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l)

The nitric acid is added first to remove any carbonate ions that might be present – they would produce a white precipitate of silver carbonate, giving a false positive result for chloride ions.

Sulfate ion SO₄^2-

• add hydrochloric acid

• add barium chloride

• white precipitate

carbonate ion CO₃²⁻

• add hydrochloric acid

• bubble through limewater

• turns cloudy

hydrogen gas

• test with a lit splint

• hear a squeaky pop

oxygen gas

• test with a glowing splint

• splint will relight

carbon dioxide gas

• bubble through limewater (calcium hydroxide)

• turns cloudy/milky

ammonia gas

damp red litmus paper turns blue

chemical test for presence of water

• add to anhydrous copper sulfate

• turns blue

physical test for pure water

• will boil at 100oc

• when heated