For The Determination Of The Formula Of A Compound From Experimental Data Lab I Had To Add Nitric Acid To A Tin

Question

For the Determination of the formula of a compound from experimental data lab, i had to add nitric acid to a tin

foil and heat the solution until oxide was the only remaining product. From my calculations based on the data, my experimental % is lower than my theoretical % (77.1% 78.8%)and my %error is 2.16%. How can that be explained and what are the possible reasons for error during the experiment?

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