Percentage Composition?

Question

If some of the magnesium oxide had escaped from the crucible, would your percentage composition calculation of magnesium be too high or too low? Explain.

Answer 1

Presumably you heated magnesium in a crucible, and formed magnesium oxide, weighing both before and after heating.

If some MgO had escaped, you would have had less product that you thought, ie less oxygen would have combined with the magnesium than you thought, therefore it would have seemed high in magnesium.