Common Errors in Titration

Weighing
  Solid spilled onto the electronic balance. This solid would be included in the total weight but cannot be transferred into the volumetric flask. Hence error in calculating the number of mole of chemical used.  
Titration
Set Up
  The funnel should be removed before you start the titration. Otherwise, liquid left in the funnel would drain into the burette during titration and thus affect the actual burette reading.  
  A white tile should be placed under the conical flask so that the colour change of indicator could be observed easily.

Use of pipette
and
burette
  Bubbles trapped inside the burette (or pipette). This would also affect the volume of titrant used in titration.  
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