Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: monitac on February 20, 2022, 05:07:09 PM
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I am doing my internal assessment for IB Chemistry and I just realised I has half of my calculations incorrect. However, after correcting them I got uncertainties of over 100 and 200%. I used back titration with inaccurate equipment (gradual cylinders) but still - I don't think I should have THAT high uncertainties.
I would be glad if someone helped my privately with my calculations as there is a lot of data, however, I attach a sample picture and PDF of my data as it might be enough for a mistake to be caught. The calculations are fairly simple, but there is just a lot of them and I feel a bit lost.
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I have not checked your calculations, but one thing stands out. You are subtracting two numbers of similar magnitude, with moderate uncertainties, and getting a significantly smaller number with relatively large uncertainty. You do this in 10.5 (subtracting two numbers with ca. 10% uncertainty to get an answer with ca. 40% uncertainty), then in 10.7 you take two such numbers and subtract them again, getting an answer with over 200% uncertainty. If you do this repeatedly in a multi-step calculation, the relative uncertainties will quickly increase. It is therefore important to make your initial measurements as accurate as possible - using a graduated cylinder is just not good enough.