A 1.803 g sample of gypsum, a hydrated salt of calcium sulfate, CaSO4 is heated at a temperature greater than 170 degree Celsius in a crucible until a constant mass is reached. The mass of anhydrous CaSO4 salt is 1.426g. Calculate the percent by mass of water in the hydrated calcium sulfate salt.

20.91% of the hydrated calcium sulfate salt is water

Explanation:

Step1 : Calculate the mass of H2O that evaporated

A hydrated salt has a mass of 1.803g. After heating at 170° C, this means water will evaporate, the mass of the salt is 1.426g

The difference is water that evaporated.

⇒Mass H2O of hydration = 1.803 g - 1.426g g = 0.377 g H2O

Step 2: Calculate the % of water in the hydrated calcium sulfate salt

⇒ mass of H2O = 0.377g

⇒ mass of calcium sulfate salt = 1.803g

⇒ % water in the calcium sulfate salt = (0.377 / 1.803) x 100% = 20.91%

20.91% of the hydrated calcium sulfate salt is water