Help in Chem LAB !!! Titration !!?

In the titration experiment:

a) Why is it important for the burette to be clean before using??

b) Why are air bubbles in the burette tip a possible source of error in a titration experiment? How do you remove air bubbles from the burette tip??


c) You cannot comment on the accuracy of the experimental value of the molarity of the HCl because you do not know the ....... ?


In (a) I think because then we can't get an accurate result, and in (b) the we won;t get an accurate reading of the volume

I'm not sure so I need accurate answers.

Thank you in advanced