Set Up
Prepare the unknown in solution
- Make sure the 400-mL beaker, the stirring rod, rubber policeman, and the 100-mm watch glass are clean.
- Obtain a weighing dish containing a sample of unknown substance from your instructor.
- Carefully measure the mass by difference of approximately 0.350 g or 0.800 g of unknown, as instructed by your teacher, into the 400-mL beaker.
Mass of unknown transferred to the beaker (g): 0.750 g
To make sure the measurement is accurate, you measure the mass of the sample by difference rather than putting it straight into the beaker.
4. Add 50 mL of distilled water to the beaker and dissolve the sample with gentle swirling.
5. Slowly add 5 mL of 6 M HCl to the solution in the beaker.
6. Add additional distilled water until there is about 250 mL of the solution in the beaker.
7. Cover the beaker with the 100-mm watch glass and, if necessary, store it in a safe place until you are ready to proceed with the determination.
Form the precipitate
8. Start a new experiment on the data collection system.
9. Use the buret clamp to attach the buret to the ring stand.
10. Connect the stainless steel temperature sensor to the data collection system.
11. Place the beaker with the solution on the hot plate and being heating it to about 90 degrees C. Do not allow the solution to boil because some may be lost through spattering.
12. Immerse the temperature sensor in the solution so that it is not touching the beaker.
Make sure to rinse any residue on the temperature sensor back into the beaker so that you are reacting all of the substance that you started with, and your mass is accurate.
13. Set the data collection system to monitor live data without recording.
14. When the solution has reached 90 degrees C, begin adding drop by drop, the 0.5 M BaCl2 solution from the buret into the beaker while gently swirling the solution with the rubber policeman. Make sure to not spill any of the solution.
15. When 25 to 35 mL of BaCl2 solution has been added, stop the addition and let the precipitate settle.
Collect the precipitate
16. Fold a piece of Whatman Ashless #42 filter paper and place into the funnel. Wet the paper with a few drops of distilled water so the paper sticks to the wall of the funnel.
17. Support the funnel in the ring mounted on a ring stand over a beaker or flask of sufficient size to hold all of the supernatant.