1. Analytical Chemistry PHCMp 101
Anions Identification Lab 8

2. Halides Nitrates and Nitrites
Anions Part II
Halides
Nitrates and Nitrites

3. Chloride, Bromide and Iodide
Halides
Chloride, Bromide and Iodide

4. Toxic Fumes!! Do not perform!
 Dry reactions
Cl-
Br- I-
Solid + dil. HCl
No reaction even on heating
Solid + Conc. H2SO4
HCl
2Cl- + H2SO4  2HCl + SO42-
HBr + Br2
HI I2
HCl is a colorless gas can be tested by formation of white clouds of NH4Cl when a glass rod moistened with NH4OH is held near the mouth of the test tube
Brown fumes of Br2 accompany HBr due to its oxidation by conc. H2SO4
Violet fumes of I2 accompany HI due to its oxidation by conc. H2SO4
Toxic Fumes!! Do not perform!
Stronger than HCl
TC! Throw away!

5. shake after each addition
Wet reactions
Cl-
Br- I-
S.S + AgNO3
White ppt of AgCl soluble in dil. NH4OH
Yellowish white ppt of AgBr sparingly soluble in dil NH4OH
Yellow ppt of AgI insoluble in dil. NH4OH
Chlorine water test:
S.S +
dil. H2SO4 +
2ml CHCl3 +
Cl2 water
-ve
Orange colour of Br2 in CHCl3 layer
With excess chlorine water , the organic layer becomes colorless due to the formation of HBrO3
Violet colour of I2 in CHCl3 layer
With excess chlorine water , the organic layer becomes colorless due to the formation of HIO3
S.S + FeCl3
No reaction
Brown color of I2
2I-+2Fe3+ I2 + 2Fe2+
Add Cl2 water
drop wise,
shake after each addition

6. Chlorine water test:
Special test for Br- & I- | No reaction with F- & Cl-
Sample + 2 ml dil. H2SO4 + 2 ml chloroform + drops of Cl2 water
Cl2 water
Br- I-
Few drops
2 Br- + Cl2  Br2 + 2Cl-
Yellow to reddish brown (orange)
2 I- + Cl2  I2 + 2Cl-
Violet
Excess
Br2 + Cl2  2BrCl (yellow)
Br2 + Cl2 (excess) + 2H2O  2HOBr + 2HCl (Colorless)
Br2 + 5Cl2 (excess) + 6H2O  2HBrO3 + 10HCl (Colorless)
I2 + 5Cl2 (excess) + 6H2O  2HIO3 + 10HCl (Colorless)

7. Special test for iodide:
Iodides in acid sol.(H2SO4) + Nitrite sol. OR hydrogen peroxide
oxidation of iodide
Free iodine
2I- + 2NO2- + 4H+  I2 + 2NO + 2H2O
2I- + H2O2 + 2H+ I2 + 2NO + 2H2O
I2 + chloroform shaking violet color in organic layer.
I2 gives deep blue color with starch solution.

8. In the following series {HF, HCl, HBr, HI} Why HF is the weakest acid, while HI is the strongest??
Electronegativity
Size
Stability
Tendency to lose electrons
Thus the iodide ion is easily oxidized into free iodine by loosing an electron. However there is no chemical oxidant which is powerful enough to oxidize F- into F2, as the negative fluoride ion is highly too stable to hold strongly a proton.

9. Nitrates and Nitrites
NO3-
NO2-

10. Same action of dil HCl but with violence.
 Dry reactions
Nitrate (NO3-)
Nitrite (NO2-)
Solid + dil HCl
No reaction
Brown fumes of nitrogen dioxide NO2 leaving a transient pale blue liquid
2NO2-+ 2H+→ 2HNO2 →
H2O+ NO+ NO2
2NO+O2→ 2NO2(g)
Solid + conc. H2SO4
Nitric acid is formed and some of it decompose with evolution of brown fumes of NO2 with characteristic odor
NO3- + H+ → HNO3
2HNO3→ 2NO2+ H2O+ ½O2
Same action of dil HCl but with violence.

11. 5 ml S.S +1 ml of dil. H2SO4 + 1 ml of FeSO4 (freshly prepared)
 Wet reactions
Nitrate (NO3-)
Nitrite (NO2-)
S.S + AgNO3
No ppt
White ppt from concentrated solution (AgNO2)
S.S + 3 ml dil. H2SO ml KI + few drops of starch solution
No reaction
I2 is liberated which impart blue color to starch
NO2- + I- + 2H+→
NO + ½ I2 + H2O
Brown ring test:
5 ml S.S +1 ml of dil. H2SO4 + 1 ml of FeSO4 (freshly prepared)
Brown ring is formed at the interface (only if conc.H2SO4 is used)
Brown ring at the junction of the 2 liquids

12. FeSO4 reduces nitrate & nitrite ions into nitrogen monoxide NO.
The brown ring test :
FeSO4 reduces nitrate & nitrite ions into nitrogen monoxide NO.
Nitrate ion is not reduced except at high acidity (conc H2SO4).
Nitrite ion in contrast is easily reduced (dil H2SO4 or acetic acid).
The excess Fe2+ then combine with NO forming unstable brownish black complex [Fe(NO)]2+ which is readily decomposed by heat.
3 Fe2+ +NO3- + 4H+ → Fe3+ + NO + 2H2O
Fe2+ + NO2 + 2H+ → Fe3+ + NO + H2O
Fe2+ + NO → [Fe(NO)]2+

13. Mixture of NO3- & NO2-
Nitrite can be tested for in presence of nitrate (by treatment with dil HCl or FeSO4 in dil H2SO4)
Nitrate can not be tested in presence of nitrite since nitrite gives all reactions of nitrate
Therefore nitrite must be removed before testing for nitrate
Fe2+ + NO2 + 2 H+ → Fe3+ + NO + H2O
Fe2+ + NO → [Fe(NO)]2+ (brown ring)
Decomposion of nitrite through its brown complex by heat: [Fe(NO)]2+ → NO + Fe 2+
The liquid becomes gradually colorless. Cool add a little more acid & a little more FeSO4.
If nitrite present decomposed, addition gives no more color.
Pour conc H2SO4 to the mixture; a brown ring indicates the presence of nitrate.