Test for Anion Anion Reagent Products

decomposition / heating of NO3

- salts gas O2 and NO2 NO3

-

Brown ring test (1) Dilute H2SO4 + FeSO4 (2) Concentrated H2SO4

Brown ring.

Cl- dilute HNO3/H2SO4 + AgNO3 White precipitate,

AgCl SO4

2- dilute HCl @ HNO3 + BaCl2 @ Ba(NO3)2

White precipitate, BaSO4

decomposition / heating of CO3

2- salts CO2 gas CO3

2-

Add dilute HCl @ HNO3 CO2 gas

Reagent Anion Observation CO3

2- White precipitate soluble in dilute HNO3 Cl- White precipitate soluble in hot water.

SO42- White precipitate soluble in dilute HNO3

Pb(NO3)2

NO3- -

All anions are not coloured. Colour of a salt depends on the cation present. Colour of cationic solution: Colourless - Ca2+, Mg2+, Al3+, Zn2+, Pb2+, NH4

+

Blue - Cu2+

Green - Fe2+ Yellow/brown - Fe3+

Solubility of salts in water NO3

- salts - All soluble. SO4

2- salts - All soluble except Ba2+, Pb2+ and Ca2+ salts

CO32- salts - All insoluble except K+, Na+ and NH4

+ salts Cl- salts - All soluble except Ag+, Hg2+ and Pb2+ salts

(soluble in hot water) All K+, Na+ and NH4

+ salts are soluble.

The type of gas produced will indicate the anion present in the salt. Effect of heat on salts NH4

+ NH3 gas CO3

2+ CO2 gas + metallic oxide

except K+ and Na+ salts. NO3

- K+ and Na+ O2 + NO2- salts

others NO2 + O2 + metallic oxide SO4

2- No decomposition except Fe, Zn and Cu SO2 @ SO3 + metallic oxide.

Cl- stable except NH4Cl NH3 + HCl O2 / NO2 nitrate ion CO2 carbonate ion.

Confirmatory tests Ion Reagent Observation Pb2+ KI Yellow precipitate KCl @ NaCl White precipitate K2SO4 @ H2SO4 White precipitate NH4

+ Nessler’s Reagent Brown precipitate Fe2+ Potassium hexacyanoferrate (II)

K4Fe(CN)6 Potassium hexacyanoferrate (III) K3Fe(CN)6

Light blue precipitate Deep blue precipitate

Fe3+ Potassium hexacyanoferrate (II) K4Fe(CN)6 Potassium hexacyanoferrate (III) K3Fe(CN)6 Potassium thiocyanate, KSCN

Deep blue precipitate Greenish brown precipitate Blood red solution

Insoluble salt

Na+, K+, NH4

+ salt Not Na+, K+,

NH4+ salt

Titration method by

neutralization reaction

(acid + alkali)

Reactions between: (acid + Solid) 1. Acid + insoluble base 2. Acid + Metal 3. Acid + carbonate

Filtration (use filtrate) Salt solution

- Boiling (1/3 of original volume) - Cooling (Crystallisation) - Filtration (use residue) - Wash/rinse with distill water - dry with filter paper

Salt crystals

Precipitation method by double decomposition

reaction (salt solution + salt solution)

- Filtration (use residue) - Wash/rinse with distill water - dry with filter paper

Example to prepare : salt solution + salt solution insoluble salt + salt solution __ __ + __ __ __ __ + __ __

Method of salt preparation

Soluble salt

Colour of Metallic Oxide from heating of salt White salt yellow (hot) and white (cool) Zn2+

White salt brown (hot) and yellow (cool) Pb2+ Blue/green salt black Cu2+ Green/yellow salt brown Fe2+/Fe3+

Test for Cation Reagent Observation Ion

- No change NH3 NH4+

- Blue precipitate insoluble in excess NaOH.

Cu2+

- Dirty green precipitate insoluble in excess NaOH.

Fe2+

- Brown precipitate insoluble in excess NaOH.

Fe3+

- White precipitate insoluble in excess NaOH.

Ca2+, Mg2+

NaOH(aq)

CaM PAZ

- White precipitate soluble in excess NaOH.

Zn2+, Al3+, Pb2+

- No visible change Ca2+

NH4+

- Blue precipitate soluble in excess NH3 Deep blue solution

Cu2+

- Dirty green precipitate insoluble in excess NH3.

Fe2+

- Brown precipitate insoluble in excess NH3.

Fe3+

- White precipitate insoluble in excess NH3.

Pb2+, Mg2+,

Al3+

NH3(aq)

Ca MPA Z

- White precipitate soluble in excess NH3.

Zn2+

Definition 1. A salt is an ionic compound which results when the

hydrogen ion in an acid is replaced by a metallic or ammonium ion (NH4

+) from a base. 2. Qualitative analysis is a series of tests conducted

on a chemical substance to identify the unknown component or components in it.

QUALITATIVE ANALYSIS OF SALT To identify cation and anion in unknown salt X. Cation : Ca2+, Mg2+, Al3+, Zn2+, Fe2+, Fe3+, Pb2+, Cu2+, and NH4

+. Anion : NO3

-, CO32-, Cl-, SO4

2-.

Gas Test H2 Gives 'pop' sound when

burning splint is introduced Cl2 Turns moist blue litmus

paper to red then white O2 Rekindles glowing splint CO2 Turns lime water chalky NO2 Brown colour and turns

blue litmus paper to red SO2 Turns acidified KMnO4

from purple to colourless NH3 / HCl Form white fumes with glass rod dipped in concentrated

HCl / NH3

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