It is often possible to change a hydrate into an anhydrous compound by heating it to drive off the water (dehydration).
A 43.71 gram sample of a hydrate of Na2SO4 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 23.15 grams of the anhydrous compound remained. What is the formula of the hydrate?
Use a period instead of a dot in the formula of the hydrate.