LAB: Procedures Decomposition of a Hydrate
Name_______________________________
Date___________ Block____
You will decompose a hydrated solid to determine experimentally the number of moles of water
in one formula unit of the hydrate. You will also determine the percent yield of your
experimental value.
Solid cobalt(II) chloride hexahydrate decomposes when heated to produce solid cobalt(II)
chloride and water according to the following equation:
CoCl2 ∙ 6 H2O (s) → CoCl2(s) + 6 H2O(g)
Materials:
for each table: vial containing CoCl2 ∙ 6 H2O(s); electronic balance
for each pair of students: (on tray at center of desk)
3 clean, dry test tubes
1 test tube holder
1 50-mL beaker to be used to hold hot test tubes
1 test tube brush
paper towels
1 scoopula
Procedure:
1. Mass a clean dry test tube. Record mass in data table.
2. Add a small amount of cobalt(II) chloride hexahydrate(s) to the test tube.
3. Mass the test tube with the cobalt(II) chloride hexahydrate(s). Record the mass of the test tube
and content before heating in the data table.
4. Place the test tube into the test tube holder so that the clamp is at the mouth of the test tube.
Hold the test tube almost horizontally and gently tap the bottom of the test tube to spread the
solid evenly along the length of the test tube. Be careful not to spill any solid. If you do spill
some solid, re-mass the test tube and solid and record the correct mass in the data table.
5. Using a pale blue Bunsen burner flame (no bright cone), heat the contents to dehydration.
Be sure to keep the test tube moving back and forth at the top of the flame. When the solid is
uniformly light blue remove the test tube from the flame and stand the test tube upright in the
50-mL beaker to cool. There should be no red or violet color in any part of the solid.
6. When the test tube is cool enough to be held with a bare hand, mass the test tube and its
contents. Record the mass of the test tube and contents after heating in the data table.
7. Repeat procedure steps 1-6 for two (2) additional trials.
8. Dispose of any solid from the test tubes into the waste container on the front desk.
Clean test tube using running water and the test tube brush. Dry the test tube with paper
toweling. Leave all materials on tray as you found them.
9. Complete lab analysis. Check the scoring rubric to make sure you have completed every
calculation and have answered the analysis items completely. Attach this procedure to front
of your lab analysis BEFORE you hand in the lab.