Titration burette uncertainty

[IB1820]

Hello. I wanted to ask what the uncertainty would be for a titrated volume if I used the burette 2 times in one titration? So for the 50cm³ burette, with 0.08cm³ uncertainty for starting volume and 0.05cm³ uncertainty for any readings – would the uncertainty of 80cm³ of titrated burette solution have the uncertainty of 0.08+0.05+0.08+0.05cm³ ? Since I used it two times, refilled it two times, read it two times?

[kw0573]

I agree that 0.26 cm3 is the uncertainty if you are told to add up absolute errors for addition/subtraction. Another way to propagate uncertainties is to view each measurement as a statistical distribution and you get essentially the standard deviation of the combined distribution. An advantage in this method is that it provides better estimates for repeated measurements (umcertainties dont accumulate as fast) but it does not give an absolute range that the true value falls in between.

IB does not care which method you use, but you should be consistent with your classmates. I just mention the other popular method if you aspire to be a scientist and you may finding yourself using it