1. Analytical Chemistry PHCMp 101
Anions Identification Lab 7

2. Carbonates/Bicarbonates Sulpher anions
Anions Part I
Carbonates/Bicarbonates
Sulpher anions

3. CO32-/HCO3- Carbonates/ Bicarbonates
CO32-
Carbonates
HCO3-
Bicarbonates
Dry reaction
Effervescence occurs due to the evolution of CO2 gas
Na2CO3 +HCl  NaCl+H2CO3
H2CO3  CO2+H2O
CO2 is colorless & odorless, it can be identified by turning lime water turbid. The turbidity disappears upon prolonged passage of CO2. 
Solid + dil. HCl

4. CO32- Carbonates HCO3- Bicarbonates
CO32-
Carbonates
HCO3-
Bicarbonates
Wet reactions
White ppt. of BaCO3 soluble in mineral acids
No ppt on cold due to the formation of soluble Ba(HCO3)2. By heating or adding NH4OH it gives white ppt. of BaCO3.
Ba(HCO3)2+2NH3  BaCO3 + (NH4)2CO3
Ba(HCO3) ∆ BaCO3 + CO2+H2O
Salt Solution (S.S) +BaCl2 (or CaCl2)
S.S + AgNO3
White ppt. of Ag2CO3
which turns black by heating due to the formation of Ag2O
Ag2CO3  Ag2O +CO2
No ppt. on cold.
Theo: How to diff bet. Carbonate and bicarbonate??

5. Ex: HCl + Na2CO3  2NaCl + H2CO3
Notes:
All carbonate salts are insoluble in water;
Exceptions: Na2CO3, K2CO3, (NH4)2CO3 soluble in water.
All bicarbonate salts are soluble in water.
Displacement reaction: Stronger acid displaces the weaker acid in its salt
Ex: HCl + Na2CO3  2NaCl + H2CO3
N.B: The decomposition of carbonates and bicarbonates by dil HCl is a displacement reaction.
Any acid stronger than H2CO3 will displace it, thus acetic acid will decompose carbonates.
Acid Ka
Acetic acid CH3COOH
Ka = 1.76x10-5 Stronger
Carbonic acid H2CO3
Ka = 4.3x10-7
Hydrocyanic acid HCN
Ka = 4.79x Weaker
Boric acid H3BO3
Ka = 5.8x Weaker
No efferves.

6. Sulpher anions S2- Sulphide SO32- Sulphite S2O32- Thiosulphate
S2- Sulphide
SO32- Sulphite
S2O32- Thiosulphate
SO42- Sulphate
Dry reaction
H2S(g)
S2-+2H+  H2S
SO2(g) SO32-+2H+  H2SO3 H2SO3  SO2+H2O
SO2(g) S2O H+  H2S2O3 H2S2O3  SO2 + H2O +S
-ve
Solid
+ dil. HCl
It has offensive rotten egg odor.
NB: It has reducing property: Changes a paper moistened with acidified dichromate from orange to green
It has burnt sulfur odor.
NB: It has a reducing property: Changes a paper moistened with acidified dichromate from orange to green.
On standing or heating SO2 evolves and soln becomes turbid 
Burnt sulfur odor +
yellow ppt. of colloidal sulphur
HCL is weaker than H2SO4
HCl is stronger than H2S,H2SO3 & H2S2O3
This test can differentiate all sulpher anions

7. Turns yellow brown  black ppt of Ag2S is formed
S2-
SO32-
S2O32-
SO42-
Wet reactions
Black ppt. of Ag2S
White ppt.
of Ag2SO3
which on boiling undergoes self oxidation and reduction producing grey ppt. of metallic Ag
2Ag++ SO32- Ag2SO3
2Ag2SO ∆
2Ag +Ag2SO4+SO2
White ppt. of Ag2S2O3
Turns yellow brown  black ppt of Ag2S is formed
2Ag++ S2O32-Ag2S2O3
Ag2S2O3+H2O 
Ag2S +2H++SO42-
White ppt of Ag2SO4 (from concentrated solutions)
S.S + AgNO3

8. S.S + acidified K2Cr2O7 soln. S.S + acidified KMnO4 soln.
S2-
SO32-
S2O32-
SO42-
S.S + BaCl2
No ppt.
White ppt. of BaSO3
soluble in dil HCl
No ppt. (except from concentrated solutions)
White ppt. of BaSO4
insoluble in dil HCl
S.S + FeCl3
Black ppt. of Fe2S3
A dark red color of Fe2(SO3)3 which turns reddish brown on boiling
Purple color of complex ferric thiosulphate
Fe(S2O3)2-
fades rapidly and disappears by boiling
S.S + acidified I2 soln.
Decolorzation of I2 and soln turns turbid
Decolorization of I2
-ve
S.S + acidified K2Cr2O7 soln.
Color of K2Cr2O7
is changed from orange to green
S.S + acidified KMnO4 soln.
Decolorization of KMnO4
Theo Q.!