Page 33 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102
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Applications in Strongly alkaline solutions (2 M NaOH)
By Back Titration Technique
Determination of glycerol
C3H8O3 + 14MnO4− + 20 OH− 3CO32− +14MnO42− + 14H2O
3C = +8 -6 = -2 3C = +4 x 3 = +12
-2 to +12----------------- loss of 14 e
Eq wt glycerol = Mw / 14
Ba2+ is added to ppt manganate, to mask its green color
Acidify with H2SO4 and back titrate xss st MnO4− ≠ st H2C2O4
2MnO4− + 5H2C2O4 + 6H+ 70 o C
2Mn2+ + 10CO2 + 8H2O
II- Cerium (IV), Ce4+
Properties
- Strong oxidizing agent, E0 = +1.44 V
- Cerric solutions in sulfuric acid does not oxidize Cl− and can be
used to titrate HCl solutions of analytes
- Salts: Cerium (IV) ammonium nitrate, Ce(NO3)4.2NH4NO3
Primary standard
Its solution does not have to be standardized (if it is a pure grade)
Standard solutions and Stability
- Salt is dissolved in sulfuric acid, at least 0.1 M, to prevent pptn of
basic salts.
- Solution in sulfuric acid is indefinitely stable.
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