1. Tests involving the reagent aqueous NaOH solution
TABLE 1. COLOURED SOLUTIONS
Ion First addition of reagent Reagent in excess Comments
Pale green (Fe Dirty green ppt No further change, however at the top of
2+
) Fe2+ (aq) + 2OH- (aq) à Fe(OH)2 (s) the mixture it may turn brown on standing
This is due to oxidation of iron(II)
hydroxide to iron(III) hydroxide
Yellow (Fe3+) Rusty brown ppt No further change
Fe3+ (aq) + 3OH- (aq) à Fe(OH)3 (s)
Blue (Cu2+) Pale blue ppt No further change
2+ -
Cu (aq) + 2OH (aq) à Cu(OH)2 (s)
Bright green Blue or blue green ppt Ppt dissolves forming a bright green
(Cr3+) 3+ -
Cr (aq) + 3OH (aq) à Cr(OH)3 (s) solution
Cr(OH)3 (s) + 3OH- (aq) à[Cr(OH)6]3- (aq)
Pink Blue ppt which turns pink on standing No further change
(Co2+) Co2+ (aq) + 2OH- (aq) à Co(OH)2 (s)
Pale pink but White or cream ppt No further change, however ppt may turn
2+ -
usually Mn (aq) +2OH (aq) à Mn(OH)2 (s) brown on standing
colourless This is due to oxidation of Mn(II)
(Mn2+) hydroxide to Mn(III)oxide
TABLE 2. COLOURLESS SOLUTIONS
Ion First addition of reagent Reagent in excess Comments
2+
Ca No ppt No ppt
NH4+ No ppt No ppt
On warming, a colourless pungent gas is

2. evolved which turns blue litmus to red
NH4+(aq) +OH- (aq) à NH3 (g) + H2O(l)
Mg2+ White ppt No further change
Mg2+ (aq) + 2OH- (aq) à Mg(OH)2 (s)
Ba2+ Little or no ppt No further change
Al3+ White ppt Dissolves to form a colourless solution All three hydroxides of Zn, Al and Pb
Al3+ (aq) + 3OH- (aq) à Al(OH)3 (s) Al(OH)3 (s) + 3OH- (aq) à[Al(OH)6]3- (aq) are amphoteric and form a complex
Zn2+ White ppt Dissolves to form a colourless solution ion:- zincate, aluminate and plumbate
Zn2+ (aq) + 2OH- (aq) à Zn(OH)2 (s) Zn(OH)2 (s) + 2OH- (aq) à[Zn(OH)4]2- (aq) respectively.
Pb2+ White ppt Dissolves to form a colourless solution
Pb2+ (aq) + 2OH- (aq) à Pb(OH)2 (s) Pb(OH)2 (s) + 2OH- (aq) à[Pb(OH)4]2- (aq)
Tests involving the reagent aqueous ammonia solution
TABLE 3. COLOURED SOLUTIONS
Ion First addition of reagent Reagent in excess
Pale green (Fe Dirty green ppt No further change, however at the top of the mixture it may turn
2+
) Fe2+ (aq) + 2OH- (aq) à Fe(OH)2 (s) brown on standing
This is due to oxidation of iron(II) hydroxide to iron(III) hydroxide
Yellow (Fe3+) Rusty brown ppt No further change
Fe3+ (aq) + 3OH- (aq) à Fe(OH)3 (s)
Blue (Cu2+) Pale blue ppt Ppt dissolves to give a deep blue solution

3. Cu2+ (aq) + 2OH- (aq) à Cu(OH)2 (s) Cu(OH)2 (s) + 4NH3 (aq) à [Cu(NH3)4]2+ (aq)
Bright green Blue or blue green ppt Ppt dissolves forming a royal blue solution
(Cr3+) Cr (aq) + 3OH (aq) à Cr(OH)3 (s) Cr(OH)3 (s) + 6NH3 (aq) à[Cr(NH3)6]3+ (aq)
3+ -
Pink Blue ppt which turns pink on standing Ppt dissolves to form a brown solution which then darkens on
(Co2+) Co2+ (aq) + 2OH- (aq) à Co(OH)2 (s) standing
Co(OH)2 (s) + 6NH3 (aq) à[Co(NH3)6]2+ (aq)
The darkening is due to the oxidation of Co(II) to Co(III)
Pale pink but White or cream ppt No further change, however ppt may turn brown on standing
2+ -
usually Mn (aq) +2OH (aq) à Mn(OH)2 (s) This is due to oxidation of Mn(II) hydroxide to Mn(III)oxide
colourless
(Mn2+)
TABLE 4. COLOURLESS SOLUTIONS
Ion First addition of reagent Reagent in excess Commenets
Ca2+ No ppt No ppt
+
NH4 No ppt No ppt
2+
Mg White ppt No further change
Mg2+ (aq) + 2OH- (aq) à Mg(OH)2 (s)
Ba2+ Little or no ppt No further change
3+
Al White ppt No further change
Al3+ (aq) + 3OH- (aq) à Al(OH)3 (s)
Zn2+ White ppt Dissolves to form a colourless solution A complex ion occurs in excess
Zn2+ (aq) + 2OH- (aq) à Zn(OH)2 (s) Zn(OH)2 (s) + 4NH3 (aq) à[Zn(NH3)4]2- ammonia solution diammine zinc(II)
ion
Pb2+ White ppt No further change

4. Pb2+ (aq) + 2OH- (aq) à Pb(OH)2 (s)
TABLE 5. Tests with various reagents other than sodium hydroxide and aqueous ammonia
Test Observation Inference Comments
Silver nitrate solution White ppt means Cl- present Partial dissolution is observed by carefully looking at
in the presence of ppt dissolves to give a the amount of ppt before and after addition of the
dilute HCl or HNO3 colourless solution Ag+ (aq) + Cl- (aq) à AgCl (s) aqueous ammonia. This is usually difficult to discern
Then followed by but the colour of the ppt and fact that it does NOT
aqueous ammonia totally dissolve in aqueous ammonia would allow one
Cream ppt to make the distinction between chloride and bromide
AgCl (s) +2NH3 (aq) à[Ag(NH3)2]+ ions.
ppt partially dissolves
Yellow ppt

5. ppt remains
Br- present
Ag+ (aq) + Br- (aq) à AgBr (s)
I- present
Ag+ (aq) + I- (aq) à AgI (s)
Barium chloride or White ppt SO32- or SO42- present Dilute nitric or hydrochloric acid must be present to
barium nitrate solution prevent the precipitation of carbonates.
SO32- present
Then followed by ppt dissolves to give a SO32- (aq) + 2H+ (aq) àSO2(g) + H2O (l)
dilute HCl or HNO3 colourless solution
SO42- present
ppt remains
Addition of HCl or White ppt Pb2+ lead(II) chloride is more soluble in hot water than cold
any source of chloride Pb2+ (aq) + 2Cl- (aq) à PbCl2 (s) water. Therefore one would see a total reduction in the
ions ppt dissolves fully when amount of ppt present when mixture is warmed. As it
sometimes an mixture is warmed and cools, crystallization occurs and the true shape of the
additional test may be recrystallises to form needle crystals are seen.
to warm the mixture if shaped crystals when cool
a ppt is formed and NB lead(II) bromide gives a similar observation but
then allow to cool it is only partially soluble in hot water while lead(II)
chloride is completely soluble in hot water
Addition of aqueous Bright yellow ppt Pb2+ lead(II) iodide is more soluble in hot water than cold
potassium iodide Pb2+ (aq) + 2I- (aq) à PbI2 (s) water. A partial reduction in the amount of ppt present
solution when mixture is warmed would be seen. As it cools,
sometimes an crystallization occurs and the true shape of the crystals
additional test may be are seen. Often the crystals exhibit a “glittery” effect.
to warm the mixture if
a ppt is formed and Red-brown solution which
then allow to cool may have black particles. Potassium iodide is a reducing agent and
if a colour change is seen, then a redox
reaction has occurred and the sample has
oxidizing properties.

6. Conc. sulphuric acid to a Vigourous effervescence Cl- present Concentrated sulphuric acid is a powerful oxidizing
solid halide e.g. sodium white mixture Gas is acidic agent
chloride, sodium bromide,
sodium iodide Colourless, pungent gas Gas is hydrogen chloride
Turns blue litmus red displacement of hydrogen chloride by sulphuric
acid
NaCl + H2SO4 à HCl + NaHSO4
Br- present
Vigourous effervescence
orange/red mixture Bromide ions are strong reducing agents and a
redox reaction occurs and bromine is produced
brown, pungent gas
gas is acidic and it also bleaches which implies
the halogen is being produced
Turns blue litmus red then white
H2SO4 + 2H+ + 2Br- à Br2 + SO2 + 2H2O
I- present
Vigourous effervescence Iodide ions are strong reducing agents and a
deep purple/black mixture redox reaction occurs and iodine is produced
purple, pungent gas gas is acidic and it also bleaches which implies
the halogen is being produced
Turns blue litmus red then white
H2SO4 + 8H+ + 8I- à 4I2 + H2S + 4H2O
Addition of acidified Decolourisation i.e. from purple to Since acidified potassium manganate is an
potassium manganate colourless oxidizing agent, the sample tested must have
solution reducing properties
Addition of acidified Goes from orange to green Since acidified potassium dichromate is an
potassium dichromate oxidizing agent, the sample tested must have
solution reducing properties
Addition of dilute acid to a Effervescence Gas produced
solid sample either dilute Solid dissolves sample must be either a carbonate or a sulphite
HCl or HNO3
No effervescence
Solid dissolves Sample must be either an oxide or hydroxide
Addition of Devarda’s Effervescence Gas is basic

7. alloy to sample in presence Colourless, pungent gas evolved Gas is ammonia
of NaOH solution and turns red litmus blue NO3- ion present
warm 3NO3- + 8Al + 5OH− + 18H2O → 3NH3 +
8[Al(OH)4]−
Addition of conc H2SO4 Effervescence Gas is acidic The conc sulphuric acid reacts with the nitrate ion to
with copper turnings Blue-green solution NO2 gas produced (brown gas) form nitric acid. The nitric acid then reacts with the
present and warm Brown, pungent gas evolved NO3- ion present
Turns blue litmus red 3Cu(s) + 8HNO3(aq) --> 3Cu(NO3)2(aq) + 2NO(g) + copper turning to form nitrogen monoxide which is
4H2O(l) oxidized to nitrogen dioxide
Addition of freshly Brown ring is formed NO3- present
prepared iron(II) sulphate
solution or crystals and NO3- + 3Fe2+ + 4H+ → 3Fe3+ + NO + 2H2O
then add conc H2SO4
slowly [Fe(H2O)6]2+ + NO → [Fe(H2O)5(NO)]2+
(brown ring)