lecture 14 redox titrations. aa nalyte + bt itrant cc + dd products requirements: -one reaction...
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Lecture 14
Redox Titrations
aAnalyte + bTitrant cC + dDproducts
Requirements:
-One reaction with integer coefficients a and b
- The reaction is fast enough to perform the whole procedure in 20-40 min
- Titrant solutions are stable and their concentrations can be easily established by the simple procedures
-There is an easy way to establish the end point of titration (that is, the convenient indicator is available)
Titrant solutions are stable and their concentrations can be easily established by the simple procedures
K2Cr2O7 - no change in 30 years
Primary standard -chemical compound that you can weighand disolve to prepare solution of known concentration without standartization
Requirements: - Purity of at least 99.9%- Stable and easy to purify if necessary- Convenient to weigh- Well soluble and stable in solution- non-toxic, non-expensive
Secondary standard -solution of known concentration which was established bytitration of the primary standard
Oxidants:
CeIV
MnO4-
Cr2O72-
BrO3-
IO3-
I2
strong
Weak, selective
][
][log06.05.1
3Ce
CeE
IV
][
][log06.077.0
2
3
Fe
FeE
][
][log06.077.0
2
3
Fe
FeE
][
][log06.05.1
3Ce
CeE
IV
Emin =0.77 + 0.063= 0.95
-E(SCE)
Emax =1.5-0.060.06=1.32
-E(SCE)
Any potential in this rangeis be satisfactory
99.9%
100.1%
][
][log06.077.0
2
3
Fe
FeE
Emin =0.77 + 0.063= 0.95
OHCreHOCr 232
72 72614
23
14272
][
]][[log
6
06.036.1
Cr
HOCrE0.01 M K2Cr2O7
[Cr3+]=10-2 M[Cr2O7
2-]=10-5M[H+]=1 M
E1.3V
1.0
1.3
0.899.9%
100.1%
][
][log03.077.0
3
Tl
TlE
Emin = 0.77+0.033=0.86-E(SCE)
OHICleHClIO 223 3462
][
][]][[log
4
06.024.1
2
623
ICl
HClIOE
Emax = 1.24-0.0153=1.19
-E(SCE)
@ 1M HCl
BrO3- + 5Br- + 6H+ 3Br2 + 3H2O
NH2
SO2NH2
NH2
SO2NH2
Br Br
+ 2Br2
Starch
I
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