AP Chemistry Dr. Istone

Lab 3: Gravimetric Analysis of a Metal Carbonate

Lab Objective: In this lab we will determine the identity of a group 1 metal carbonate compound by gravimetric analysis. The unknown is weighed and dissolved in water and the precipitate is filtered, dried, and weighed. From the data the formula weight and identity of the unknown metal carbonate is determined.

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Lab Procedure:

  1. Set up the Bunsen burner and ring clamp, light the burner and heat the crucible.
  2. Add 2g of unknown carbonate to the crucible and place on the triangle.
  3. Weigh the crucible on balance and record, repeat until the mass no longer decreases.
  4. Add crucible contents to a beaker then add 200 mL water and 125 mL of solution and stir.
  5. Position filter paper in the funnel, drain water into another beaker.
  6. Transfer the precipitated material to the flask, allow the funnel to drain.
  7. Use a microspatula to school the material and set in the drying oven, allow it to cool.
  8. Weigh and record the mass of the filter paper, repeat until the mass does not change.

Pre Lab Questions: 1. 2. 3. 4. 5. Data Tables:

Mass of crucible + M2CO3| 21. 427 g| Mass of crucible + M2CO3 (dried)| 21. 325 g| Mass of crucible| 19. 403 g| Mass of M2CO3| 2. 024 g| Mass of filter paper + CaCO3| 2. 572 g| Mass of filter paper| 0. 904 g| Mass of CaCO3| 1. 668 g| Moles of CaCO3| 0. 0167 mol| Molar Mass of M2CO3| 121. 19 g/mol| Identity of M2CO3| K2CO3| Percent Error| %|

Calculations and Post Lab Analyses 1. 2. 3. 4. The molar mass would be too high if too much unknown carbonate was measured, the sample was not heated long enough, or if the calcium carbonate was not all dried out.

The molar mass could be too low if too little unknown carbonate was measured; the sample was heated too long, or if all the calcium carbonate was not completely filtered.

Conclusion: In this lab we determined the identity of a group 1 metal carbonate gravimetrically using a double-replacement precipitation reaction. The unknown was weighed and dissolve din water and then a solution of calcium chlorate was added to the metal carbonate solution to precipite the carbonate ions as calcium carbonate. The precipitate was filterted dried and weighed.