Experiment 1: Gravimetric Analysis with Calcium Chloride and Potassium Carbonate

Question

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. You will also investigate the hygroscopic nature of calcium chloride through a comparison reaction.

Place the weigh boat on the scale and determine its mass.
Add approximately 2.0 g of CaCl2 to the weigh boat (the total mass should be the mass of the weigh boat plus 2.0 g). Set this sample aside, and let it sit exposed to the air (but otherwise undisturbed) for 24 hours. Complete Steps 3 - 20 while you wait..
Place a 250 mL beaker on the scale. Tare the scale and leave the beaker on the scale..
Add approximately 2.0 g. of CaCl2 to the beaker. Record the exact mass of the powder in Table 1.
Remove the beaker from the scale. Use a pipette to add 50 mL of distilled water to the beaker and mix with the stir rod until all CaCl2 has dissolved.
Note: This is an exothermic process, so the beaker may become warm.

Place a 50 mL beaker on the scale. Tare the scale and leave the beaker on the scale.
Add 2.5 g of K2CO3. Record the exact mass of the powder in Table 1.
Remove the beaker from the scale. Use a pipette to add 25 mL of distilled water to the 50 mL beaker and mix with the stir rod until all K2CO3 has dissolved.
Add all of the K2CO3 solution to the beaker containing the CaCl2 solution. It is important that all of the K2CO3 is added. To ensure this, rinse the 50 mL beaker with up to 5 mL distilled water, and pour the rinse in the CaCl2 solution.
Stir the solution for approximately four minutes. Then, allow it to sit for 15 minutes. This gives sufficient time for all CaCO3 to precipitate.
While the solution is sitting, set up the filtration apparatus. Begin with an iron ring and a ring stand. Secure the ring to the stand. Be sure to select the ring size that most appropriately holds the funnel.
Place a funnel in the ring, and place a 250 mL Erlenmeyer flask below the ring, such that the bottom of the funnel is also inside the mouth of the flask.
Obtain a piece of filter paper. Use the scale to weigh the filter paper and record the mass in Table 1.
Obtain a watch glass. Use the scale to weigh the watch glass
Be sure not to lose any product during this transfer.
Repeat Steps 3 - 20 for the CaCl2 that was allowed to sit exposed to air for 24 hours.
Allow the products from both trials to dry, undisturbed, for at least 24 hours and 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.

Explanation / Answer

Step 1: Calculate the number of moles of reactants

For Cacl2=2/112=0.017moles

For K2CO3 = 2.5/138 = 0.018moles

step 2: here limiting reagent is CaCl2

Step 3: as per reaction Cacl2 + K2CO3 = CaCO3 + 2KCl

so one mole Cacl2 produce one mole of  CaCO3 = 0.017 moles of Cacl2 produce 0.017moles of  CaCO3

Step 4: molar mass of CaCO3 = no of moles X molecular weight of substance

   = 0.017X100

= 1.7g of CaCO3

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