Sn + 4 HNO₃ → SnO₂ + 4 NO₂ + 2 H₂O
Heating was required to get rid of the H₂O. When all moisture is gone,
you weigh the sample. After which, you further heat it to get ride of the
oxygen. By doing this, you would know the individual mass of each
element. Then, you can solve for the empirical formula of the oxide of
tin.
Hope this helps best of luck :)
