ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
PRACTICAL CHEMISTRY
IDENTIFICATION OF GASSES
1. H2 (Hydrogen) : A colourless , odourless neutral gas is evolved which
burns with a pale blue flame producing a pop sound.
2. O2 (Oxygen) : A colourless, odourless neutral gas is evolved which
rekindles a glowing splinter and turns colourless alkaline pyrogallol
solution to brown.
3. H2O (Water) : A colourless, odourless neutral gas is evolved which turns
white anhydrous copper sulphate blue and turns blue cobalt chloride paper
pink.
4. CO2 (Carbon dioxide) : A colourless , odourless acidic gas is evolved which
turns lime water milky but has no effect on acidified KMnO4 OR acidified
K2Cr2O7 solution.
5. SO2 (Sulphur dioxide) : A colourless , suffocating odour acidic gas is
evolved which turns lime water milky and turns acidified KMnO4 solution
pink to clear colourless and acidified K2Cr2O7 solution orange to clear
green.
6. Cl2 (Chlorine) : A greenish yellow , pungent odour acidic gas is evolved
which turns moist starch iodide paper blue black.
7. HCl (Hydrogen chloride) : A colourless , pungent odour acidic gas is
evolved which gives dense white fumes when a glass rod dipped in
ammonia solution is brought near gas.
8. H2S (Hydrogen Sulphide) : A colourless , rotten egg smell acidic gas is
evolved which turns moist lead acetate paper silvery black.
9. NO2 (Nitrogen dioxide) : A reddish brown, irritating odour acidic gas is
evolved which turns moist KI paper brown.
10. NH3 (Ammonia) : A colourless pungent odour basic gas is evolved which
gives dense white fumes when a glass rod is dipped in conc. HCl is brought
near the gas.
How to identify basic radicals or cations?
(a)By using flame test
(1) Sodium ion [Na+] – Golden yellow flame
(2)Potassium ion [K+] – Lilac flame
(3)Calcium ion [Ca2+]– Brick red flame
(4) Copper ion [Cu2+] – apple green flame
(b) By using NaOH and NH4OH (wet test)
Radical DropwiseNa Excess NaOH Dropwise Excess
OH NH4OH NH4OH
ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
Fe2+ Dirty green Dirty green Dirty green ppt Dirty green
Ferrous or ppt ppt ppt
Iron(II)
Fe3+ Reddish Reddish Reddish brown Reddish
Ferric or brown ppt brown ppt ppt brown ppt
Iron(III)
Cu2+ / Cuprous or Pale blue ppt Pale blue ppt Pale blue ppt Deep blue
Copper (II) soln.
Ca2+ Milky white Milky white No reaction No reaction
Calcium ion ppt ppt
Pb2+ Chalky white Soluble Chalky white Chalky white
Lead ion ppt ppt ppt
Zn2+ Gelatinous Soluble Gelatinous Soluble
Zinc ion white ppt white ppt
Please note :
1. Precipitate of Zn(OH)2 is soluble in excess NaOH and NH4OH solution.
2. Precipitate of Cu(OH)2 is soluble in excess NH4OH solution only.
3. Precipitate of Pb(OH)2 is soluble in excess NaOH solution only.
4. To distinguish between Zn2+ and Pb2+ ions only NH4OH solution is used.
(c)Identification of Ammonium [NH4+]
Test - Add NaOH solution in the ammonium salt and heat.
Obs - It gives pungent smelling gas which gives dense white fumes when
glass rod dipped in Conc. HCL is brought near the gas.
Inference - Gas is Ammonia
II) How to identify acidic radicals or anions?
(a)Sulphur dioxide [SO2]–
Anion can be identified –sulphite(SO32-) and bisulphite (HSO31-)
Test –add dilute sulphuric acid and test the gas.
Obs -Gas turns lime water milky and decolourises the pink colour of the
KMnO4 solution. Or It can also turns orange acidified Potassium
dichromate to clear green solution.
(d) Carbon dioxide [CO2]–
ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
Anion can be identified – Carbonate (CO32-) and bicarbonate (HCO31-)
Test – add dilute sulphuric acid and test the gas.
Obs – Gas turns lime water milky and do not show any changes to the
colour of KMnO4 solution and K2Cr2O7 solution.
(e)Hydrogen Sulphide [H2S]–
Anion can be identified – Sulphide (S2-)
Test –add dilute sulphuric acid and test the gas with the moist lead
acetate
paper.
Obs – Gas turns moist lead acetate paper silvery grey and also has rotten
egg smell.
(f) Chlorine [Cl2]–
Anion can be identified – Chloride (Cl-)
Test – add Manganese dioxide and Conc. Sulphuric acid then observe the
gas and check the impact over moist starch iodide paper.
Obs – Greenish yellow coloured gas turns moist starch iodide paper bluish
black.
(g) Nitrogen dioxide [NO2]–
Anion can be identified – Nitrate (NO3-)
Obs–Reddish brown gas turns moist starch iodide paper brown.
Test – add copper fillings and Conc Sulphuric acid and test the gas with
the
help of starch iodide paper.
Note – This test can also be done by only heating (dry test ) but
Ammonium nitrate, Sodium nitrate and Potassium nitrate does not
give NO2 gas by dry test. Thus brown ring test is done.
(h) Hydrogen [H2] –
Obs – gives pop sound sound when burning splinter is brought near the
gas.
(i) Oxygen [O2] –
Obs -rekindles the glowing splinter.
(j) Bromine vapours [Br2] -
Obs -brown coloured vapours get decolourise when comes in contact with
ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
unsaturated hydrocarbon i.e. ethene and ethyne.
(k) Ethene [C2H4] -
Obs - decolourises brown colour of bromine./ do not any specific
observation when passed through ammoniacal cuprous chloride
solution or ammoniacal silver nitrate solution.
Test –pass the gas through bromine solution.
(l) Ethane [C2H6]–
Obs–does not decolourise bromine
Test – pass the gas through bromine solution.
(m) Ethyne [C2H2] –
Obs–decolourises bromine solution / forms red ppt when passed through
ammoniacal cuprous chloride solution / forms white ppt when passed
through ammoniacal silver nitrate solution.
Test – 1) pass through bromine solution
2) pass through ammoniacal silver nitrate solution or ammoniacal
cuprous chloride solution.
(n) Ammonia [NH3]–
Cation can be identified – Ammonium ion (NH4+)
Obs – 1) gives dense white fumes when glass rod dipped in Conc HCL is
brought near the gas.
2) forms pale brown solution in Nessler’s reagent when added in a
small amount but when passed in excess it forms dark brown ppt.
III) Colour of some important compounds/metals/non metals –
a) Copper [Cu] – reddish brown or Brownish pink
b) Copper oxide / cupric oxide [CuO]– black colour powder
c) Copper sulphate hydrated [CuSO4.5H2O]– blue crystals
d) Anhydrous Copper sulphate [CuSO4 ]–white amorphous powder
e) Manganese dioxide [MnO2]– black colour powder
f) Copper chloride [CuCl2]/ Copper nitrate [Cu (NO3)2] – bluish green
g) Lead oxide [PbO] – Buff yellow
h) Lead [Pb] – Silvery grey
i) Lead dioxide [PbO2] – litharge or yellow residue
j) Zinc oxide [ZnO]–white residue when cold but yellow when hot
k) Ferrous sulphate [FeSO4] – Light green
Note – ‘Moist’ should be mentioned before any paper used for the chemical test.
ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
Eg- Moist lead acetate paper, Moist starch iodide paper.
IV) Solubility chart -
Soluble Insoluble Exceptions
Salts of sodium,
Potassium and
Ammonium
All Chloride, Iodide or AgCl, PbCl2, Hg2Cl2
bromide salts.
All Sulphites and Ag,Pb, Hg
Sulphates
All Sulphides Na, K, NH4+
All Nitrates
All Carbonates Na, K, NH4+
All Hydroxides Gr. IA, Ca
All Oxides Na, K, NH4+
V) Few examples of distinguishing compound by using Chemical test –
1)
Sodium Sulphate Sodium Sulphite
Test – Add Bacl2 solution to both the solution and observe
Obs - White ppt observed which is Obs - White ppt observed which is
insoluble in Conc. Hydrochloric acid dissolves in Conc. Hydrochloric acid.
Other option for the same sets of salt
Test – Add dil. Sulphuric acid and observe the gas
ICSE-X CHEMISTRY BY MOHAN BHATT 917 222 8888
Obs - No specific observation Obs - Gas evolves which turns lime
water milky and decolourises Pink
KMnO4 solution.
2)
Zinc Sulphide Zinc Nitrate
Test – Add dil. Sulphuric acid and observe the gas.
Obs - Rotten egg smelling gas evolves Obs - No Specific observation
which turns moist lead acetate paper
silvery black.
Other option for the same sets of salt
Test – Heat both the sample in dry test tube separately and observe
Obs - Salt fuses Obs - Reddish brown gas evolves which
turns moist starch iodide paper brown.
3)
Sulphur dioxide Carbon dioxide
Test – Pass both the gases to lime water and KMnO4 solution.
Obs - Lime water turns milky and Obs - Lime water turns milky but no
decolourises KMnO4 solution change to KMnO4 solution
4)
Potassium nitrate / Potassium Sodium nitrate / Sodium chloride
chloride
Test – Perform flame test
Obs - Lilac flame observed Obs - Golden yellow flame observed
5)
Lead nitrate Zinc nitrate
Test – Add NaOH solution to both the solutions.
Obs - Chalky white ppt observed Obs - Gelatinous ppt observed which
dissolves in excess of NaOH solution. dissolves in excess of NaOH solution
6)
Cupric oxide (CuO) Manganese dioxide (MnO2)
Test – Add Conc. HCl is added to both the sample.
Obs - Bluish green solution is formed Obs - Sample remains black in colour.
