Determining the Percent Composition of a Hydrated Compound - Part II
1. Find the mass of a clean, dry evaporating dish. Record your mass in the data table below.
2. Add a piece of the potassium aluminum sulfate hydrated compound to the dish and record the mass of the evaporating
dish and the compound in the data table below.
3. Place the evaporating dish on the hot plate and heat gently. This time you need to use a lower heat setting. Using
crucible tongs and a stirring rod, gently heat the compound until you begin to see water being removed from the
crystals. Once the water is removed you need to continue to heat the solid until it is a white solid with no clear
crystalline pieces left. (BE CAREFUL NOT TO BURN THE COMPOUND)
4. Remove the evaporating dish from the hot plate using the crucible tongs and allow it to cool on the wire gauze.
5. Once the dish and the anhydrate are completely cool, weigh them and record in the data table below.
6. Once you have finished weighing the product add a small amount of water to the evaporating dish and stir to try and
dissolve the crystals. Once most of the crystals are dissolved pour the solution and any undissolved solid into a clean
labeled weighing boat and set aside.
Data Table:
Mass of clean, dry evaporating dish
Mass of dish and KAl(SO4)2 hydrate
Mass of KAl(SO4)2 hydrate
Mass of dish and KAl(SO4)2 anhydrate
Mass of KAl(SO4)2 anhydrate
1. Calculate the mass of the KAl(SO4)2 hydrate and put it in the data table above.
2. Calculate the mass of the KAl(SO4)2 anhydrate and put it in the data table above.
3. Calculate the mass of water that was removed by heating the hydrate.
4. Calculate the moles of water.
5. Calculate the moles of KAl(SO4)2 anhydrate.
6. Determine the empirical formula of this hydrated compound.