Conceptual Chemistry Lab: Determination of a Hydrate
Name: ___________________________
Introduction
Most ionic solids have crystal lattice structures that have water coordinated in the crystal. Calcium
chloride, for an example, has two water molecules coordinated in its crystal, and its formula is:
CaCl2∙2H2O. In this lab, we are going to investigate the amount of water that is attached in a crystal of
Magnesium Sulfate in order to determine its actual hydrate formula.
Procedures
1. Record the mass of an empty, clean crucible: _________________ g
2. Add 2.00 grams of Magnesium Sulfate to the crucible: ______________ g
3. Add the mass of the Magnesium Sulfate to the mass of the crucible: _______________ g
4. Set up a ring stand, Bunsen burner with a triangle (See Figure 1). We will not use the lid this
time.
Figure 1: Ring stand set up for a crucible and triangle.
5. Heat the crucible with the Magnesium Sulfate for 10 minutes. Then, allow the crucible to cool.
6. Record the final mass of the crucible: _________________
7. Calculate the change in mass of the crucible (Take Step 3 – Step 6) : ___________________
8. The difference that you calculated in step 7 is the amount of water that has been boiled out of
the crystal of Magnesium Sulfate. Determine the number of moles of water that was boiled out
of the crystal ______________________
9. Determine the grams of magnesium sulfate there are left (without water). Take Step 6 – Step 1:
______________________
10. Write the formula for magnesium sulfate: _______________. Determine its molar mass:
_____________________
11. Determine the number of moles of magnesium sulfate for step 9: ______________
12. Determine the number of water molecules per one formula unit of magnesium sulfate by
dividing your mole value in step 8 by the mole value in step 11: _________________
13. Record your formula here for the hydrate for magnesium sulfate: ________________