Gravimetric Analysis of a Metal Carbonate
1.
Mass about 2.00 grams of an unknown metal carbonate (M2CO3) into a massing dish. Record
the exact mass of the carbonate in the data table.
2. Transfer the carbonate sample to a 400 mL beaker.
3. Add 200 mL DI H2O to the line marked on the container labeled “DI H2O 200 mLs”. Add the DI
H2O from the container to the 400 mL beaker containing the carbonate.
4. Using the magnetic stirrer stir contents of 400 mL beaker to dissolve all of the carbonate.
5. While waiting for the carbonate to dissolve transfer 100 mL of 0.20 M CaCl2 solution to the 100
mL graduated cylinder.
6. After all of the carbonate has dissolved, add the 0.20 M CaCl2 SLOWLY in 10 mL increments
using the 10 mL graduated cylinder while continuing magnetic stirring.
7. After all the CaCl2 solution has been added continue to stir for one minute. Then turn stirrer
“off” and remove beaker from the stirrer. Remove stir bar from beaker using technique shown
in class. Allow beaker contents to settle for 10 minutes.
8. While waiting for the beaker contents to settle, mass a piece of filter paper and record its mass
in the data table. Place the massed filter paper in the Buchner vacuum filtration funnel.
Moisten the filter paper with squirts from the DI H2O wash bottle.
9. Make sure the filtration funnel is snuggly positioned in the 500 mL filtration flask. At the end of
the 10 minutes, turn on the cold water to start the vacuum filtration.
10. As soon as vacuum filtration has been started immediately pour the liquid mixture from the 400mL beaker into the filtration funnel. Keep the liquid level below the top of the funnel.
11. Swirl the 400 mL beaker to suspend the precipitated CaCO3, and use the DI wash bottle to rinse
the inside of the beaker. Transfer this mixture to the funnel. Rinse the beaker with small squirts
from the DI wash bottle and transfer these to the filter.
12. When all of the solid has been transferred to the filter, rinse the CaCO3 precipitate (on the filter
paper) with 3 small portions of DI H2O. Allow all the liquid to aspirate, and then turn off the cold
water.
13. Remove the top half of the Buchner filtration system as demonstrated in class. Using the paper
clip, “poke” up from the bottom of the funnel to loosen the filter. Use a microspatula to
carefully transfer the filter cake to a watch glass. If needed, use microspatula to transfer any
CaCO3 residue to the top of the filter cake. Record watch glass # in data table.
14. Place watch glass and filter cake in oven overnight.
15. Use tongs to remove watch glass and dried CaCO3 cake and permit to cool on ceramic pad.
16. When cool, weigh filter paper and the solid CaCO3 and record mass in data table.
POST-LAB Calculations and Analysis
1.
Calculate the moles of precipitated CaCO3 and record in data table.
2. Calculate the molar mass of the unknown carbonate and enter in data table.
3. From the calculated molar mass, identify the unknown.
4. Review procedure and list possible sources of error that would cause the molar mass to be too
high or too low.
Mass of M2CO3
_______g
Mass of filter paper
_______g
Mass of watch glass and #
_______g #________
Mass of filter paper, watch
glass, and CaCO3
_______g
Mass of CaCO3
_______g
Moles of CaCO3
_______
Molar mass of M2CO3
_______g/mol
Identity of M2CO3
_______