A1.20 gram sample of a hydrated salt is heated to a constant mass of .80 gram. what is the percent of mass of water contained in the original sample

The mass of the water is 1.20 - 0.80 = 0.40 grams.

The % of water is (0.40 / 1.20 ) * 100 = 33 1/3% 

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.

Go ask spider man