Why are different pipettes used between dilutions?

You must change pipette tips between each serial dilution because trace amounts of solutions will stick to the side of the pipette tip, which can affect concentrations of dilutions.

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.