20 March 2013
Indirect gravimetric determination of hydrate compound in a mixture Objective
To determine the percent BaCL2*2H2O in sample of hydrated mixture. Materials:
Gravimetric balance(electronic weighing scale)
Crucible without cover
Iron Support stand
Wire mat, glove
Step 1. Support a clean porcelain crucible and its cover on a clay triangle (see Figure 1). Heat them in the hottest portion of a burner flame until the bottom of the crucible glows dull red for five minutes. Expelling water from the hydrate.
Step 2. Allow the crucible and cover to cool to room temperature. (NOTE: continue to Step 3 while waiting for them to cool.)
Step 3. Give a clean test tube to your laboratory instructor in exchange for a test tube containing a mixture of your unknown sample of BaCl2•2H20 and another substance. Record the unknown Identity Number on the REPORT FORM (3).
Step 4. (NOTE: Always handle the crucible with clean tongs.) When the crucible and cover are cool, weigh them together to the nearest 0.001 g and record this mass on the REPORT FORM (4).
Step 5. Use tongs to remove the cover and pour all of your sample in the crucible. weigh the crucible, sample to the nearest 0.001 g. Record this value on the REPORT FORM (5).
Step 6. Use tongs to carefully place the crucible, cover and sample back on the clay triangle and tilt the cover slightly to allow moisture (gas) to escape.
Step 7. Heat the crucible gently at first but gradually increase the heat. Heat the crucible in the hottest portion of the flame until the bottom glows dull red for 10 minutes.
Step 8. Use tongs to carefully place the lid on straight and allow the system to cool to room temperature.
Step 9 Weigh the crucible, cover and residue to the nearest 0.001 g and record this value on the REPORT FORM (9).
Step 10. Repeat steps 6-9. If the difference in...