Important Observations and Chemical Tests

Test for lead ion (Pb²⁺ ion)

[ Sample : lead nitrate solution or lead acetate solution]

Reagent	Precipitation formed	Colour of ppt
H2SO4 or Na2SO4	PbSO4	White ppt insoluble in dil acid.
HCl	PbCl2	White ppt soluble in hot water
H2S	PbS	Black ppt soluble in conc. HNO3
K2CrO4	PbCrO4	Yellow ppt insoluble in dil. Acetic acid
KI	PbI2	Yellow ppt formed which dissolves in boiling water to a colourless solution, which deposits as brilliant yellow crystals upon cooling.
NaOH	Pb(OH)2	Chalky white ppt , dissolves in excess NaOH solution.
NH4OH	Pb(OH)2	Chalky white ppt , dissolves in excess NH4OH solution.

Test for Silver ion (Ag⁺)

[ Sample: silver nitrate solution]

Reagent	Precipitation formed	Colour of ppt
NaCl or HCl	AgCl	Curdy white ppt, soluble in ammonium hydroxide but reappears on adding HNO3.
KI	AgI	Yellow ppt insoluble in ammonium hydroxide.

Test for Copper ion (Cu²⁺)

[ Sample : copper sulphate solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Cu(OH)2	Pale blue ppt, insoluble in excess NaOH solution.
NH4OH	Cu(OH)2	Pale blue ppt, soluble in excess NH4OH solution to produce an inky blue solution.
K4[Fe(CN)6]	Cu2[FeCN)6]	Chocolate brown ppt.
H2S	CuS	Black ppt.

Cu+ ion	Cu2+ ion
When NH4OH solution is added a pale blue ppt is formed which dissolves in excess to form an inky blue solution.	When NH4­OH solution is added a pale yellow ppt is formed which dissolves in excess to form a colourless solution.
Cu(OH)2 when heated produce a black residue of CuO.	Cu2(OH)2 when heated produce a red residue of Cu2O.

Test for Ferrous ion (Fe²⁺)

[ Sample : ferrous sulphate solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Fe(OH)2	Dirty green ppt, insoluble in excess NaOH solution.
NH4OH	Fe(OH)2	Dirty green ppt, insoluble in excess NH4OH solution.
K4[Fe(CN)6]	K2Fe[Fe(CN)6]	Bluish white ppt formed which turns deep blue due to aerial oxidation.
K3[Fe(CN)6]	KFe[Fe(CN)6]	Deep blue ppt.(Turnbull’s blue)

Test for Ferric ion (Fe³)

[ Sample : ferric chloride solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Fe(OH)3	Reddish brown ppt, insoluble in excess NaOH solution.
NH4OH	Fe(OH)3	Reddish brown ppt, insoluble in excess NH4OH solution.
K4[Fe(CN)6]	KFe[Fe(CN)6]	Deep blue ppt.(Prussian blue)
K3[Fe(CN)6]	Fe[Fe(CN)6]	Brown colouration.
NH4SCN	Fe(SCN)3	Blood red coluration

Test for Aluminium ion (Al³⁺)

[ Sample : aluminium nitrate solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Al(OH)3	Gelatinious white ppt formed which dissolves in excess NaOH solution.
NH4OH	Al(OH)3	Gelatinious white ppt formed which is insoluble in excess NH4OH solution.

Test for Zinc ion (Zn²⁺)

[ Sample : zinc nitrate solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Zn(OH)2	Gelatinious white ppt formed which dissolves in excess NaOH solution.
NH4OH	Zn(OH)2	Gelatinious white ppt formed which dissolves in excess NH4OH solution.
K4[Fe(CN)6]	K2Zn3[Fe(CN)6]2	Bluish white ppt formed.
(NH4)2[Hg(SCN)4] + CuSO4	Zn[Hg(SCN)4]+ Cu[Hg(SCN)4]	Violet ppt formed.

Test for Calcium ion (Ca²⁺)

[ Sample solution contain zinc nitrate solution]

Reagent	Precipitation formed	Colour of ppt
NaOH	Ca(OH)2	White ppt formed which is insoluble in excess NaOH solution.
Oxalic acid	CaC2O4	Crystalline white ppt

Test for Anions:

Experiment	Observation	Inference
Sample solution is treated with lead nitrate solution	Black ppt of lead sulphide produced.	S2- ion
Sample solution is treated with sodium nitroprusside solution.	Violet colouration	S2- ion
Sample solution is treated with Silver nitrate solution.	Curdy white ppt of silver chloride soluble in NH4OH solution but reappears on adding HNO3.	Cl– ion
Sample solution is treated with Silver nitrate solution.	Pale yellow silver bromide ppt produced which dissolves in excess NH4OH	Br– ion
Sample solution is treated with Silver nitrate solution.	Yellow ppt of silver iodide produced which is insoluble in NH4OH	I– ion
Sample solution is treated with Silver nitrate solution.	White ppt of silver thiosulphate produced which changes to yellow to orange to red to brown to black.	S2O32- ion
Sample solution is treated with BaCl2 solution.	White ppt barium sulphate produced which is insoluble in dil. HCl.	SO42‑ ion
Sample solution is treated with BaCl2 solution.	White ppt of barium sulphite produced which is soluble in dil. HCl.	SO32- ion
Sample solution is treated with calcium chloride solution.	Crystalline white ppt of calcium oxalate formed.	C2O42- ion
Sample solution is treated with lead acetate solution	Yellow ppt lead chromate produced insoluble in acetic acid but soluble in dil HNO3.	CrO42- ion
Sample solution is treated with silver nitrate solution	Reddish brown ppt of silver chromate produced.	CrO42- ion
Sample solution is treated with ferric chloride solution	Deep red colouration which produce a reddish brown ppt on heating.	CH3COO– ion

Test for different gases:

^{1.Test for Carbon dioxide gas}

Carbon dioxide is a colorless and odourless gas which turns lime water milky but cannot change the orange colour of acidified potassium dichromate solution.

2.Test for Sulphur dioxide gas

Sulphur dioxide is a suffocating smelling colourless gas which turns lime water milky and turns acidified potassium dichromate solution green from orange.

3.Test for Chlorine gas

It is a greenish yellow gas with bleaching powder like smell which turns Starch KI paper Blue black.

4.Test for Ammonia gas

It is colourless pungent smelling gas. It turns nessler’s Reagent brown.

5.Test for Hydrogen sulphide gas

It is a colourless gas with a rotten egg smell. It turns lead nitrate solution black.

6.Test for Oxygen gas

It turns alkaline pyrogallol solution brown

7.Test for hydrogen

Pure hydrogen gas burns with a pale blue flame.

8.Test for Nitrogen dioxide

It is a reddish brown gas. It turns green acidified ferrous sulphate solution brown.

9.Test for water vapour

1. It turns white anhydrous copper sulphate to blue ( copper sulphate pentahydrate).
2. It also turns blue cobalt chloride paper pink.

Heating effects

1.Heating copper carbonate

When light green copper carbonate is heated, black copper oxide is produced along with carbon dioxide gas.

2. Heating zinc carbonate

When white zinc carbonate is heated, zinc oxide is produced which is yellow when hot and white when cold along with carbon dioxide gas.

3. Heating sodium carbonate decahydrate

When white crystalline solid is heated, a white anhydrous sodium carbonate is formed along with water vapour.

4. Heating copper sulphate pentahydrate

When blue crystalline copper sulphate pentahydrate is heated, white amorphous anhydrous copper sulphate is formed.

5. Heating zinc nitrate

When white zinc nitrate is heated, zinc oxide(which is yellow when hot and white when cold), nitrogen dioxide and oxygen is produced.

6. Heating copper nitrate

When blue copper nitrate is heated, black copper oxide, nitrogen dioxide and oxygen is produced.

7. Heating lead nitrate

When white lead nitrate is heated, yellow lead oxide, nitrogen dioxide and oxygen is produced.

8. Heating Iodine

When grey colour solid iodine is heated, violet vapour of iodine is produced.

9. Heating ammonium dichromate

Orange red ammonium dichromate when heated produce greenish grey chromic oxide, nirogen gas and water.

Test for Acids

1.Test for Hydrochloric Acid

i)When hydrochloric acid is added to colourless silver nitrate solution, curdy white ppt of silver chloride is produced which dissolves in ammonium hydroxide solution.

ii)When Hydrogen chloride gas comes in contact with a glass rod dipped in ammonium hydroxide solution, a dense white fumes of ammonium chloride is produced.

2. Test for Sulphuric acid

i) When colourless barium chloride solution reacts with sulphuric acid, a white ppt of barium sulphate is produced which is insoluble in dilute HCl.

ii) When lead acetate or lead nitrate solution is added to sulphuric acid, a white ppt of lead sulphate is produced.

3. Test for Nitric acid

Nitric acid is treated with freshly prepared ferrous sulphate. Then the test tube is cooled in running tap water. After that, conc.sulphuric acid is added along the side of the test tube. A prominent brown ring is formed at the junction of the two liquids.

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