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4.
The oxidation-reduction titration method is divided into different methods according to the type of titrant used
(1) Potassium permanganate method-determination of oxygen consumption in drinking water
1) Potassium permanganate method
The oxidizing ability of MnO 4 - is related to the acidity of the solution
In slightly acidic, neutral or weakly alkaline solutions, the semi-reaction formula is
After the reaction, brown MnO 2 is formed , which hinders the observation of the end point
Therefore, the strong oxidizing property of KMnO 4 is often used as a titrant, and different reaction conditions can be used according to the nature of the substance to be measured in the water sample
2) Preparation and calibration of potassium permanganate standard solution
KMnO 4 reagent contains a small amount of MnO 2 and other impurities
In order to prepare a more stable KMnO 4 solution, weigh a little more than the calculated amount of KMnO 4 and dissolve it in a certain volume of distilled water, for example, to prepare 0.
The standard materials for calibrating KMnO 4 mainly include Na 2 C 2 O 4 , H 2 C 2 O 4 · 2H 2 O, (NH 4 ) 2 Fe(SO 4 ) 2 · 6H 2 O, As 2 O 3 , pure iron wire, etc.
3) Oxygen consumption and its measurement
a.
Experimental phenomenon: If there are more organic matter, the purple will fade; if there are few organic matter, the purple will not change much
b.
In the formula: C 1 —— KMnO 4 standard solution concentration (1/5KMnO 4 ), mol/L;
V 1 ——The amount of KMnO 4 standard solution added at the beginning , ml;
V 1 '——the amount of KMnO 4 standard solution consumed during titration , ml;
C 2 —Na 2 C 2 O 4 standard solution concentration (1/2Na 2 C 2 O 4 ), mol/L;
V 2 ——The amount of Na 2 C 2 O 4 standard solution added , ml;
V water -the volume of the water sample, ml;
8-Conversion factor of oxygen
.
c.
Matters needing attention:
Eliminates [CI - ] interference plus of Ag 2 SO .
4 precipitation masking
.
· Measures to speed up the reaction: increase the concentration of reactants- excess KMnO 4 ; increase the temperature-100°C reaction, 80°C titration; add catalyst Mn 2+ during titration
.
Related Links: Titration Analysis-Redox Titration (2)
