the system as CO2(g). Therefore, the first titration step titrates both the oxalate and the vanadium.
1. Dissolve about 0.3 g (weighed accurately) of the complex salt in at least 60 ml of
sulfuric acid (2 M). Dilute this solution to 100 ml with distilled water. This step destroys the complex, liberates C2O4
2– and produces
VO2+, both of which can be titrated with KMnO4.
2. Take a 25 mL aliquot and heat the solution to about 80°C on a hot plate.
3. Titrate this hot solution with potassium permanganate (0.01 M) until a bright pink colour is first seen and doesn’t fade on standing for about 30 seconds.
The vanadium must be reduced back down in order to perform a second KMnO4 titration this time
with just the vanadium being oxidised as there is no oxalate left in the system. The reduction is
achieved by reacting the oxidised vanadium with sodium sulfite. To ensure there is no excess
sodium sulfite to interfere with the second half of the titration the solution is boiled to drive off SO2.
4. Add approximately 0.1 g of sodium sulfite to the oxidised solution and then boil the solution
for 5 minutes until all SO2
is expelled and then titrate at ~ 60°C
IN THIS PROCESS, 1. how do I caculate the moles of oxalate from the difference between first and second titrations. 2, Calculate the no of moles of vanadium from second titration??
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