The purpose of the experiment was to determine the percent calcium carbonate in a heterogeneous mixture and to determine the molar volume of carbon dioxide gas at standard temperature and pressure. Theories explored for the experiment included heterogeneo

        Techniques used in the experiment included: cleansing and rinsing glassware, preparation of sample, the saturation of water with CO2, the set up of the CO2 collection apparatus, set up of the CO2 generator, and the determination of volume, temperature, and pressure of the CO2 gas.

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The hypothesis stated that the molar volume of carbon dioxide gas at STP can be determined by the fabrication of gas generator; the hypothesis was accepted since the molar volume of carbon dioxide gas at STP was determined to be 25.44L/mol.

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  Materials and Methods:

        For materials and methods used in the above mentioned experiment refer to the Laboratory Manual for Principles of General Chemistry (pages. 175 – 182). Divergences from the original procedure included: The mass of CaCO3 was given as less than 1g, not calculated as stated in the manual. 6g of NaCO3 and 60ml of vinegar were used to saturate the water with CO2, not an Alka-Seltzer as stated in the manual.

Results:

Table #1: Mass

Table #2: Determination of Volume, Temperature and Pressure of the CO2 gas

                                                                                       

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Table #3: Mass of Carbon Dioxide Evolved

Table #4: Molar Volume  of CO2 Gas

Table #5: Percent CaCO3 in mixture

Calculations:

Table #2:

• Volume of CO2 collected: 38ml – 19ml = 19ml
• Pressure of “dry” CO2: 763.78torr – 23.8torr = 739.98torr

Table #3:

• Mass loss of generator = mass CO2 evolved: 167.62g – 167.41g = 0.21g

                                                                                                                                       

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Table #4:

• Pressure of “dry” CO2:  739.98torr/760torr = 0.97atm
• Volume of CO2 at STP: (0.97)(0.019)(273)/(298)(1) = 0.0168L
• Moles of CO2 generated: (0.97)(0.0168)/(0.0821)(298) = 6.6x10-4mol
• Molar volume of CO2 at STP: 0.0168L/6.6x10-4mol = 25.45L/mol
• Average molar volume of CO2 at STP: (25.45 + 25.44 + 25.45)/3 = 25.44L/mol

Table #5:

• Moles of CaCO3 in sample: 6.6x10-4mol
• Mass of CaCO3 in sample: 6.6x10-4 x 100g/mol / 1molCaCO3 = 0.066g
• Percent of CaCO3 in sample: 0.066/0.083 x 100 = 79.5%
• Average percent of CaCO3 in sample: (79.5% + 82.9% + 79.5%)/3 = 80.6%

Discussion:

        After the experiment was performed, the percent calcium carbonate in a mixture and the molar volume of carbon dioxide at STP were determined. As stated in table #4, the average volume of carbon dioxide at STP was 25.44L and as stated in table #5 the average percent of CaCO3 in sample was 80.6%. From the obtained results it was seen that the experiment was performed adequately; the volume of CO2 was slightly higher than what it should have been for an ideal gas as stated in the manual. By applying the principles and concepts of gasses learned, such as the ideal gas law and Dalton’s law of partial pressures, logical results were obtained through experimentation. By looking at the reaction equation, it was seen that the reaction between CaCO3 and HCl was completed in a successful way since CO2 was given

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off as a product and its volume was measured and recorded. The percent error in the experiment was 13.5%; it could be due to experimental errors mentioned later. Even though some experimental errors could have been present during the conduction of the experiment, they were not severe errors since the obtained results lied between logical and expected ranges.

        

   Conclusion:

        The results obtained from the experiment were: : The percent calcium carbonate in the mixture was 80.6% and the average molar volume of CO2 gas at standard temperature and pressure was 25.44L/mol with a percent error of 13.5%. The hypothesis stated that the molar volume of carbon dioxide gas at STP can be determined by the fabrication of gas generator; the hypothesis was accepted since the experiment proved that the molar volume of CO2 gas at STP can be determined by the above mentioned procedures.

        Experimental errors that could have altered the results obtained include: The use of different balances for each trial performed could have caused divergences in the measurements of different masses. Another error would be not saturating the water with CO2 before conducting the experiment; this would alter the results since some CO2 gas would be lost during experimentation because of its solubility in water. A defective gas generator could also cause incorrect results by loss of CO2 gas, or inaccurate techniques applied during the reaction of CaCO3 with HCL.

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        Improvements which could help in experimentation include: the use of the same balance throughout the experiment, accurate and consistent techniques applied during the process of evolving the CO2 gas and ensuring the quality of materials being used for the experiment.

                                                                                                                                         

                                                                             

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Reference:

Beran, J.A. (2009). Laboratory Manual for Principles of General Chemistry. New Jersey. John Wiley & Sons, Inc.

Brown, Bursten, LeMay. (2000). Chemistry: The Central Science. New Jersey. Prentice-Hall, Inc.

Zumdahl, Zumdahl. (2009). Chemistry. Boston, MA. Houghton Mifflin Company.

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Post-laboratory Questions:

1. If the water is not saturated, the volume of CO2 would be reported too low since we would loose CO2 gas because of its solubility in water. This would make the percent of CaCO3 in the sample to be reported too high.
2. This poor laboratory technique will affect the reported percent CaCO3 because the reaction which gives of CO2 gas is happening before the CO2 gas can be collected thus the volume of CO2 cannot be measured properly affecting the reported percent CaCO3.
3. If a small crack is present in the rubber stopper, the molar volume of CO2 would be reported too low because some of the CO2 given off by the reaction of HCL and CaCO3 would escape through the crack in the rubber stopper.
4. If the water level is higher inside the cylinder than outside the cylinder, the “wet” CO2 gas pressure would be less than atmospheric pressure. B) If an adjustment is made to equilibrate the water levels, the volume of the “wet” CO2 gas would increase because as pressure increases, volume also increases, they are directly proportional. C) If the student chemist does not equilibrate the water levels, the number of moles of CO2 generated in the reaction would be reported higher than what it actually is.
5. If an air bubble accidentally enters the CO2 collection graduated cylinder after the reaction is completed, the moles of CO2 collected would be affected because the volume of CO2 would be reported too high, if the volume is reported high, the moles would be reported too high as well.

                                                                                                                       

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6. If a large amount of calcium sulfate is present in the original sample, the molar volume of the CO2 would not be affected since we do not use the mass of the original sample to calculate the molar volume of CO2. b) This would affect the percent of CaCO3 in the sample in the sense that it would be reported too low since we would need more CaCO3 to produce CO2 at STP.