Random facts about random stuff:
1. Why should you use potassium manganate (VII) instead of potassium dichromate (VI) during titration of FeSO4?
A1:Because KMnO4 changes from purple to colourless when reduced, so that only the yellow colour from the Fe2(SO4)3 that is being oxidised can be seen. On the other hand, K2Cr2O7 changes from orange to green, which is exactly what you don't want because the original colour of FeSO4 is green.
A2: Because although KMnO4 is dangerous (with health rating of 3/4 and reactivity rating of 3/4) concentrations used in the lab would at most leave a near unwashable stain. On the other hand, K2Cr2O7 is carcinogenic (with health rating of 4/4 and reactivity rating of 1/4). Which one would you prefer?
2. Why must you do titration at least 3 times?
A: First time to zam all the way until its over the end point but somewhere there. The second time is to zam until near the end point and then do slowly until the end point is reached. The third time is for faking your results so that your value seem to be very consistent. (Not a good idea if the teacher is staring at your throughout the session.)
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