By: Howard Andres

In this lab experiment, our lab group’s purpose was to identify a compound by mass relationships.  We were given an unknown compound, and we had to determine whether it was either a carbonate of Na₂CO₃ or K₂CO₃, or whether it was a hydrogen carbonate of NaHCO₃ or KHCO₃.  By using the quantitative observations we would receive during the course of our experiment, we would be able to determine first whether if the compound was a carbonate or hydrogen carbonate.  Then, we would be able to compare the ratios of the mass of solid chloride we would receive in the experiment with either the carbonate or hydrogen carbonate we received.  By comparing this ratio to the theoretical ratios we would get by using the compounds’ molar masses, we would find that whatever compound’s theoretical ratio was closest to our actual ratio, that would be the identity of our unknown compound.

Several observations were made during the experiment.  Most of them are recorded in the qualitative observations portion of the lab report.  Basically though, our group took notice of how violent the effervescence was when 6 molar HCl was dropped onto the unknown compound.  There were many bubbles, and some splattering occurred when the compound was heated.  Additionally, we observed of how after the first heating, loss of mass in the sample was minute, leading to the results we made.

As a result of such a small difference in mass of the sample after the first heating, 0.08g, our group concluded that our unknown was a carbonate.  After converting it to a solid chloride with the HCl, we found the ratio of its mass to the dry carbonate as .92:1.  Comparing this ratio to the theoretical ratios we got if the sample was a carbonate, we found that the mass ratio of KCl:K₂CO₃, 1.093:1, was closer to our actual ratio than the mass ratio of NaCl:Na₂CO₃, with it being 1.103:1.  As a result, this led us to the conclusion that the identity of our unknown sample was the carbonate K₂CO₃.

Our experiment went pretty well, but there were probably a few errors.  One was that of the splattering of the compound when heated with the HCl, which probably reduced the mass of the compound, which would thereby affect our results.  Another possible error is that we did not heat or cool the compound for the 10 minute periods that the written procedure stated, but rather cut them down to 5 minute periods.  This loss of time in heating and cooling could probably have had an affect upon the masses we got of the compounds, which would affect our results.  Overall though, the experiment to identify a compound with mass relationships went well.

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