An acid-base titration is performed but some base that splashed onto the sides of the flask is not rinsed down prior to the endpoint measurement. Will the calculated molarity of the acid sample be erroneously high or low, and why?

The calculator will be erroneously high.

If we imagine a titration between HCl and NaOH.

We use a ##1moldm^-3## sample of HCl to workout the concentration of a 25ml sample of NaOH, just to make things easy imagine that the C of the NaOH is also ##1moldm^-3##, you would expect to need 25ml of the HCl to neutralise the NaOH.

However, if you do not wash down the HCl and 1ml collects on the sides, the readings from the beurette will be 26ml.

##c=n/v## We know ratio is 1:1 in the reaction, So ##26*10^-3 *1 = 0.026##

##0.026/0.025=1.04##

So because of the excess HCl on the side of the beaker, the calculation tells us that the NaOH's concentration is ##1.04moldm^-3## when actually it is ##1moldm^-3##