Why do you add water to the reaction product and heat again before recording the final mass?

Question

Lab 8, Empirical formula of Magnesium oxide.

Answer 1

Not sure of your exact procedure or experimental design, but I'm guessing you have synthesized magnesium oxide and want to find the final mass produced. You would dissolve the final product in water in an attempt to get rid of any soluble impurities, since MgO is not soluble. After adding the water, you'd of course want to filter that solution to obtain the MgO again, and then dry it completely to obtain as accurate a mass as possible.