What effect will it have on my results????

[zibb3r]

So this was the experiment we did for the determination of the the iron content in fertiliser:


1. collect previousy standardised KMnO4 in a 100ml beaeker.

2. Rinse all conical and volumetric flasks with deionised water

3. Accurately weigh X grams of fertiliser and transfer to volumetric flask

4. Measure out 10 or 20 mls of H2SO4 and add this to the flask

5. Add 20ml deionised water to solution, mix and then filter to remove insoluble compunds.

6. Return filtrate to volumetric flask and invert to mix

7. Rinse pipette with fertiliser soln and transfer 20ml aliquots to 3 conical flasks
'
8. Rinse and fill burette with the KMnO4 and record initial volume. 

9. Titrate until rxn is observed and record results

10. Repeat until concrodancy is achieved

So If the burette was rinsed with water instead of permanganate solution what effect would this have on the results? and why?

My teacher said the result would be too low, but why???

THanks

[Somye]

so if you washed your burette with water, the concentration of the permanganate would be lower, and hence you would need a greater titre in order to complete the redox reaction. Then, as you would need a higher titre, you would have a higher calculated mol of the iron, and hence an inflated value for the percentage composition