Experiment 2
Gravimetric Determination of Water of Hydration

PROCEDURES

1. Clean two crucibles and lids using soap, water and test tube brush. Rinse with water and dry with a paper towel.

2. Set up a ring stand with 2 rings and place a Bunsen burner under each ring. Adjust the height of the rings to about 2 inches above the top of the Bunsen burners. Place a clay triangle on each of the rings. Then carefully light both Bunsen burners.

3. Using crucible tongs, place the crucibles with their lids on the clay triangles and heat intensely for 10 minutes to dry the crucibles.

4. Allow the crucibles to cool for one minute and, using crucible tongs, place them in a desiccator for 10 minutes or until they reach room temperature.

5. Keep crucible and lid together as a matched pair throughout the entire experiment. Each matched pair will have its own column of data on the data page.

6. Using crucible tongs, transfer a matched pair to the balance. It is important to use the same balance throughout the experiment. Weigh and record the mass to 3 decimal places on the data page. NOTE: Using crucible tongs prevents mass inaccuracies due to contamination of the crucibles and lids with oil and moisture from the skin.

7. Place slightly more than one gram of the sample in each crucible. Weigh and record the mass to 3 decimal places on the data page. Place the matched pair in the desiccator using crucible tongs.

8. Repeat steps 5 and 6 for the other matched pair.

9. Place each matched pair on a clay triangle. Heat with a Bunsen burner using a low flame for five minutes. NOTE: The low flame prevents spattering of the sample during dehydration. If spattering occurs, mass may be lost when the crucible and lid are transferred from the ring to the desiccator.

10. Gradually increase the temperature of the flame until you are using a medium flame and continue heating for an additional ten minutes. CAUTION: DO NOT ALLOW CRUCIBLES OR SAMPLES TO BECOME RED HOT SINCE UNDESIRED SAMPLE DECOMPOSITION MAY OCCUR.

11. Allow the crucibles to cool 1 minute and then place them in a desiccator for 10 minutes or until they reach room temperature.

12. Weigh each matched pair and record the mass to 3 decimal places on the data page.

13. Heat again for 10 minutes on medium heat. Cool in desiccator, weigh to 3 decimal places and record on the data page. If the mass is not within 0.005 g of the previous mass, repeat this step until the mass is within 0.005 g.

14. Record your results on the "master data sheet" provided by your instructor.

15. Residue in the crucibles should be placed in the labeled waste container.

NOTE: Always perform weighings on the same balance so that constant errors will cancel out. Always use crucible tongs to handle your crucibles.