Back Titration Errors

[pHysiX]

Hey guys. I was wondering if u could post up wat sorts of errors and how they affect the final percentage of something you are analysing in a back titration.

I did a back titration, and I somehow got a percentage of Nitrogen higher then the manufacturer...n the only reason so far is that I've titrated too much...I need more reasons. Please help. Any errors that would result in a lower or higher percentage will be appreciated heaps!

[gfb]

-The burette and pipette must be rinsed with the solutions that are to deliver.

-The conical flask must be rinsed with distilled water.

-If equipment is incorrectly rinsed immediately prior to use, the calculated unknown concentration will not accurately represent the true value (i.e manufacturer)

Hope I helped..

[kurrymuncher]

ummm, these are just a few general errors:

parallax errors- reading burette and pipette
equipment not being rinsed properly with appropriate solutions before titration
standard solution may react to a small extent with chemicals like CO2 etc (not very likely)

[Gloamglozer]

Sources of uncertainty:

1.  You did not exactly dispense everything in the pipette because you saw (or supposed to have seen) droplets of liquid on the walls of the pipette.
2.  Depending on what you analysed, the thing you analysed may have impurities in them.

[pHysiX]

thanks for all the responses so far =]