SALTS : A QUALITATIVE ANALYSIS

Meaning : chemical technique used to identify the ions present in a salt by analyzing its physical and chemical properties and hence determine the identity of the salt.

Steps to identify :o Initial observation : colouro Action of heat : the gas released (possibility of anion)

: Color of solid when hot and cold if heated (possibility of cation)o Make aqueous solution to test for cations (using NaOH and NH3) Color of precipitate

Solubility and color if excess o Confirmatory tests for cations (Pb2+, Fe2+, Fe3+, NH4+)

Anions (CO32-, NO3

-, SO42-, Cl-)

INITIAL OBSERVATION : COLORSalt Anion Solid Aqueous

Copper (II); Cu (II) NO3-, SO4

2-, Cl- Blue BlueCO3

2- Green InsolubleIron (II), Fe (II) NO3

-, SO42-, Cl- Green Green

Iron (III), Fe (III) NO3-, SO4

2-, Cl- Brown Brown

ACTION OF HEAT : GAS EVOLVED (Possibility of the anion)

ACTION OF HEAT : COLOR WHEN HOT AND COLD (Possibility of the cation from the color of solid when hot and cold, possibility of anion from the gas evolved)Carbonate CO3

2- Nitrate NO3-

Ammonia

Sulphate SO42- Chloride Cl-

ADDING NaOH AND NH3 : Identifying the cations

Zn2+ can be identified compared to Pb2+ and Al3+ it ppt in NH3 and dissolved in excess (colorless) Ca2+ can be identified from Mg2+ no ppt for Ca2+ in NH3

To identify between Pb2+ and Al3+ use confirmatory test for Pb2+ (as below)

CONFIRMING THE ANIONS

CONFIRMING THE CATIONSCation Method ConclusionIron (II) and iron (III)

-add 2 cm3 of potassium hexacyanoferrate (II) to 2 cm3 of X solutionOR-add 2cm3 of potassium hexacyanoferrate (III) to 2 cm3 of X solutionOR-add 2 cm3 of potassium thiocyanate to 2 cm3 of X solution

potassium hexacyanoferrate (II)

Pale blue precipitate

Iron (II) present

Dark blue precipitate

Iron (III) present

potassium hexacyanoferrate (III)

Dark blue precipitate

Iron (II) present

Greenish brown solution

Iron (III) present

potassium thiocyanate Pale red Iron (II) presentBlood red Iron (III) present

Lead (II) -2 cm3 of KCl is added to 2 cm3 of X-diluted with 5 cm3 of distilled water-heated up then cool with running tap water

OR-same method but change KCl to KI

1. white precipitate formed, disappears when heated but appears when cold2. Equation :3. White precipitate is PbCl2 which is soluble in hot water but insoluble in cold

*If use KI, yellow precipitate appears when cold, PBI2