Experiment 1: Gravimetric Analysis with Calcium Chloride and Potassium Carbonate In this experiment, proper analytical experimental techniques will be utilized to perform a double displacement reaction. A solution will be prepared containing a known quantity of calcium chloride. Then, the mass of calcium present will be determined through a careful precipitation of calcium carbonate.
Materials 250 ml Beaker 50 ml Beaker 4.0 g Calcium Chloride, CaCl 2 250 ml Plastic Erlenmeyer Flask (2) Filter Papers Funnel 100 ml Graduated Cylinder Pipette 5.0 g Potassium Carbonate, K 2CO 3 Scale Stir Rod Watch Glass Weigh Boat *Camera/Smart phone is Sufficient *170 ml Distilled Water *10 ml Isopropyl Alcohol *Stopwatch or Timer *You Must Provide Procedure 1. Put on your safety glasses and gloves (provided in your safety box).
2. Turn on the scale by pressing the button labeled 0/T. If your scale does not turn on, you may have to remove the battery cover and remove a small strip of plastic from the battery housing. Once the scale is on, press the 0/T button a second time to zero the scale. Make sure that the units are in grams (g). If not, press the M button until the units displayed are in grams. 3. Place a weigh boat on the scale and zero the mass of the weigh boat by pressing the 0/T button. Your scale should now read 0 g. 4. Add 2.0 g of CaCl 2 to the weigh boat. Set this sample aside, and let it sit exposed to the air (but otherwise undisturbed) for 24 hours. Complete Steps 5-20 while you wait. 5. Place a 250 ml beaker on the scale and zero it. 6. Measure another 2.0 g of CaCl 2 to the beaker. Record the exact mass of the powder in Table 1. 7. Remove the beaker from the scale. Use a 100 ml graduated cylinder to measure and pour 50 ml of distilled water into the beaker and mix with the stir rod until all the CaCl 2 has dissolved. Note: This is an exothermic process, so the beaker may become warm. 8. Place a 50 ml beaker on the scale and zero the scale. 9. Add 2.5 g of K 2CO 3 to the 50 ml beaker. Record the exact mass of the powder in Table 1. 10. Remove the beaker from the scale. Use the 100 ml graduated cylinder to measure and pour 25 ml of distilled water into the 50 ml beaker. Mix with the stir rod until all the K 2CO 3 has dissolved. 11. Rinse the stir rod with water. 12. Add all of the K 2CO 3 solution to the beaker containing the CaCl 2 solution. It is important
that all of the K 2CO 3 is added to the beaker. To ensure this, rinse the 50 ml beaker with up to 5 ml distilled water, and pour the rinse in the CaCl 2 solution. 13. Using the stopwatch to keep time, stir the solution with the stir rod for four minutes. Then, allow it to sit for 15 minutes. This will allow sufficient time for the chemical reaction to occur. 14. Rinse the stir rod with water. 15. Place a piece of filter paper on the scale and record the mass in Table 1. 16. Place a watch glass on the scale and record the mass in Table 1. 17. Fold the filter paper in half and in half again so that it resembles a triangle with one arched side. 18. Pull apart one fold of the filter paper so that three sides of the filter paper remain together, with one side making up the other half of the funnel shape. 19. Hold the funnel over a sink or any sized container. Place the paper into the funnel and use a pipette to drip 5 ml of distilled water around the edges of the filter paper. This will prevent the filter paper from rising up out of the funnel. 20. Rest the funnel on top of the Erlenmeyer flask. 21. After 15 minutes has passed, swirl the beaker and slowly filter the solution (that you created in Step 9) from the 250 ml beaker through the filter paper. Additional distilled water may also be used to transfer any remaining solid into the filtration apparatus. 22. After all the solution has been filtered, use the pipette to rinse the filter paper with approximately 5 ml of isopropyl alcohol to aid the drying process. Allow the isopropyl alcohol to completely drip through the filter before removing filter paper from the funnel. 23. Carefully remove the filter paper. Unfold and place it precipitate-side up onto the preweighed watch glass. Be sure not to lose any precipitate during this transfer.
24. Allow the precipitate to dry, undisturbed, for at least 24 hours. Determine the mass of the product recovered by re-weighing the system and subtracting the weight of the filter paper and watch glass. Record your data in Table 1. 25. Use your camera (or smart phone) to take a picture of the results. Be sure to correctly label the picture and send it to your instructor along with the answers to the lab questions.