Important Observations and Chemical Tests

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Important Observations and Tests
Important Observations and Tests

Test for lead ion (Pb2+ ion)

[ Sample : lead nitrate solution or lead acetate solution]

ReagentPrecipitation formedColour of ppt
H2SO4 or Na2SO4PbSO4White ppt insoluble in dil acid.
HClPbCl2White ppt soluble in hot water
H2SPbSBlack ppt soluble in conc. HNO3
K2CrO4PbCrO4Yellow ppt insoluble in dil. Acetic acid
KIPbI2Yellow ppt formed which dissolves in boiling water to a colourless solution, which deposits as brilliant yellow crystals upon cooling.
NaOHPb(OH)2Chalky white ppt , dissolves in excess NaOH solution.
NH4OHPb(OH)2Chalky white ppt , dissolves in excess NH4OH solution.
Lead Sulphate
White ppt of lead sulphate
Lead Chloride
Crystalline white ppt of lead chloride
lead sulphide
Black ppt of lead sulphide
lead chromate
Yellow ppt of lead chromate
lead iodide
Yellow ppt of lead iodide
lead hydroxide
White ppt of lead hydroxide

Test for Silver ion (Ag+)

[ Sample: silver nitrate solution]

ReagentPrecipitation formedColour of ppt
NaCl or HClAgClCurdy white ppt, soluble in ammonium hydroxide but reappears on adding HNO3.
KIAgIYellow ppt insoluble in ammonium hydroxide.
silver chloride
Curdy white ppt of silver chloride
 silver iodide
Yellow ppt of silver iodide

Test for Copper ion (Cu2+)

[ Sample : copper sulphate solution]

ReagentPrecipitation formedColour of ppt
NaOHCu(OH)2Pale blue ppt, insoluble in excess NaOH solution.
NH4OHCu(OH)2Pale blue ppt, soluble in excess NH4OH solution to produce an inky blue solution.
K4[Fe(CN)6]Cu2[FeCN)6]Chocolate brown ppt.
H2SCuSBlack ppt.
Cu+ ionCu2+ ion
When NH4OH solution is added a pale blue ppt is formed which dissolves in excess to form an inky blue solution.When NHOH 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.
copper hydroxide
Pale blue ppt of copper hydroxide
copper ferrocyanide
Chocolate brown ppt of copper ferrocyanide
copper sulphide
Black ppt of copper sulphide

Test for Ferrous ion (Fe2+)

[ Sample : ferrous sulphate solution]

ReagentPrecipitation formedColour of ppt
NaOHFe(OH)2Dirty green ppt, insoluble in excess NaOH solution.
NH4OHFe(OH)2Dirty 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)
ferrous hydroxide
Dirty green ppt of ferrous hydroxide

Test for Ferric ion (Fe3)

[ Sample : ferric chloride solution]

ReagentPrecipitation formedColour of ppt
NaOHFe(OH)3Reddish brown ppt, insoluble in excess NaOH solution.
NH4OHFe(OH)3Reddish 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.
NH4SCNFe(SCN)3Blood red coluration
Ferric hydroxide
Reddish brown ppt of
Ferric hydroxide
Prussian blue ppt
Prussian Blue ppt
ferric thiocyanate
Blood Red colouration of ferric thiocyanate

Test for Aluminium ion (Al3+)

[ Sample : aluminium nitrate solution]

ReagentPrecipitation formedColour of ppt
NaOHAl(OH)3Gelatinious white ppt formed which dissolves in excess NaOH solution.
NH4OHAl(OH)3Gelatinious white ppt formed which is insoluble in excess NH4OH solution.
aluminium hydroxide
Gelatinious white ppt of aluminium hydroxide

Test for Zinc ion (Zn2+)

[ Sample : zinc nitrate solution]

ReagentPrecipitation formedColour of ppt
NaOHZn(OH)2Gelatinious white ppt formed which dissolves in excess NaOH solution.
NH4OHZn(OH)2Gelatinious white ppt formed which dissolves in excess NH4OH solution.
K4[Fe(CN)6]K2Zn3[Fe(CN)6]2Bluish white ppt formed.
(NH4)2[Hg(SCN)4] + CuSO4Zn[Hg(SCN)4]+ Cu[Hg(SCN)4]Violet ppt formed.
zinc hydroxide
Gelatinious white ppt of
zinc hydroxide
Zinc ferrocyanide
Bluish white ppt of Zinc
ferrocyanide

Test for Calcium ion (Ca2+)

[ Sample solution contain zinc nitrate solution]

ReagentPrecipitation formedColour of ppt
NaOHCa(OH)2White ppt formed which is insoluble in excess NaOH solution.
Oxalic acidCaC2O4Crystalline white ppt
 calcium hydroxide
White ppt of calcium hydroxide
calcium oxalate
Crystalline white ppt of calcium oxalate

Test for Anions:

ExperimentObservationInference
Sample solution is treated with lead nitrate solutionBlack ppt of lead sulphide produced.S2- ion
Sample solution is treated with sodium nitroprusside solution.Violet colourationS2- 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 NH4OHBr ion
Sample solution is treated with Silver nitrate solution.Yellow ppt of silver iodide produced which is insoluble in NH4OHI 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 solutionYellow ppt lead chromate produced insoluble in acetic acid but soluble in dil HNO3.CrO42- ion
Sample solution is treated with silver nitrate solutionReddish brown ppt of silver chromate produced.CrO42- ion
Sample solution is treated with ferric chloride solutionDeep red colouration which produce a reddish brown ppt on heating.CH3COO ion
 silver chromate
Reddish brown ppt of silver chromate
ferric acetate
Deep red colouration of ferric acetate

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.

Lime water Test for Carbon dioxide
Lime water Test for Carbon dioxide

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.

Chlorine gas
Chlorine gas
Starch iodide test
Starch iodide test

4.Test for Ammonia gas

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

Nessler's Turning brown
Nessler’s Turning brown

5.Test for Hydrogen sulphide gas

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

 Black Lead Sulphide
Black Lead Sulphide

6.Test for Oxygen gas

It turns alkaline pyrogallol solution brown

Alkaline progallol
Alkaline progallol turns brown

7.Test for hydrogen

Pure hydrogen gas burns with a pale blue flame.

 Pale Blue flame of hydrogen
Pale Blue flame of hydrogen

8.Test for Nitrogen dioxide

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

Nitrogen dioxide gas
Nitrogen dioxide gas

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.
white anhydrous copper sulphate to blue ( copper sulphate pentahydrate).
white anhydrous copper sulphate to blue ( copper sulphate pentahydrate).
blue cobalt chloride paper  turns pink
blue cobalt chloride paper turns pink

Heating effects

1.Heating copper carbonate

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

copper carbonate
copper carbonat

copper oxide
copper oxide

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.

 Zinc carbonate
Zinc carbonate
Zinc oxide
Zinc oxide

3. Heating sodium carbonate decahydrate

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

 white crystalline Sodium carbonate decahydrate
white crystalline Sodium carbonate decahydrate
White amorphous anhydrous sodium carbonate
White amorphous anhydrous sodium carbonate

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.

zinc nitrate
zinc nitrate

6. Heating copper nitrate

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

Copper nitrate
Copper nitrate

7. Heating lead nitrate

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

  White lead nitrate
White lead nitrate

8. Heating Iodine

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

    Solid Iodine
Solid Iodine
 Iodine vapour
Iodine vapour

9. Heating ammonium dichromate

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

Ammonium dichromate
Ammonium dichromate
     Chromic oxide
Chromic oxide
Heating ammonium dichromate
Heating ammonium dichromate

Test for Acids

1.Test for Hydrochloric Acid

 Hydrochloric Acid
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.

dense white fumes of ammonium chloride
dense white fumes of ammonium chloride

2. Test for Sulphuric acid

Sulphuric Acid
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.

White ppt of barium sulphate
White ppt of barium sulphate

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
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.

 Ring Test
Ring Test

Bibliography

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