Question

Whenever I titrate during chemistry practicals my 1st titre value is always higher than my rough titre and the 2nd and 3rd would be concordant with my rough titre. Any contribution to why this is the case would be appreciated.
When using the pipette do you allow the tip to touch the surface of the base or wait for the last drop?

Answer 1

Pipette come in two types and each pipette should be marked as to the type it is. One type will have TC on the bulb or at the suction end. That means "to contain" and in those you touch the pipette to the glass, then blow out the liquid left after it has drained. The second type has a TD on the bulb or at the suction end. That stands for "to deliver". On these you touch the tip of the pipette to the glass (say the beaker) and allow it to deliver whatever it will. The liquid remaining in the pipette STAYS THERE and is not allowed to be delivered.

About the titer, I can't speculate. Make sure the buret tip on the delivery end does not have a bubble in it before titration begins.That would cause the first buret reading to higher than any of the subsequent ones.