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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

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                                                                                                                                  Godoy 1

Dr. Donald Baird

Supraja Kolluri

Daniella Godoy

Partner: Tiffany Medina

April 2, 2009

Calcium Carbonate Analysis; Molar Volume of Carbon Dioxide

ABSTRACT:

        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 heterogeneous mixture, molar volume, standard temperature and pressure, Dalton’s law of partial pressures and the deal gas law among other concepts. The percent of calcium carbonate and the molar volume of carbon dioxide gas were determined by the fabrication of a gas generator; the mass of the sample was measured and the volume of CO2 gas evolved was measured. The results obtained 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.

                                                                                                                                              Godoy 2

        The purpose of the experiment was to calculate the percent calcium carbonate in a mixture and to calculate the molar volume of carbon dioxide gas at standard temperature and pressure (STP). During the conduction of the experiment several theories were examined; some theories included: molar volume, which could be described as the volume of 1 mole of an ideal gas at STP (22.4L) (Zumdahl, 2009). In the case of the above mentioned experiment, carbon dioxide was used; CO2 was not an ideal gas so the molar volume was calculated to be 25.44L/mol. The fact that CO2 was not an ideal gas was why the results obtained were slightly different from 22.4L. Standard temperature and pressure was 273oF and 1atm. Another concept explored was Dalton’s law of partial pressure which stated that the total pressure of various gasses equals the sum of each pressure exerted by each gas (partial pressure) (Beran, 2009). In the above mentioned experiment, Dalton’s law of partial pressure was used to determine the pressure of “dry” carbon dioxide and it represented by: Pco2 = Pt – Ph2o. The concept of the ideal gas law was represented by the equation PV = nRT which could be referred to as a combination of Boyle’s law and Charles’ law. In the experiment, the ideal gas equation was used to determine the amount of moles of CO2 generated. Finally the concept of a heterogeneous mixture was explored during the experiment. A mixture is said to be heterogeneous if the mix of the substances is not uniform (Brown, Bursten, LeMay, 2000). That was the case with the mixture between the calcium carbonate and the acid. The reaction equation used in the experiment was: HCL + CaCO2 → CO2 + H2O + CaCl2

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.

                                                                                                                                              Godoy 3

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.

                                                                                                                                              Godoy 4

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

Trial 1

Trial 2

Trial 3

Mass of Sample

0.083g

0.082g

0.087g

Mass of generator + sample before reaction

167.62g

167.58g

167.47g

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

Trial 1

Trial 2

Trial 3

Initial volume of water in "CO2 collecting cylinder"

38ml

31ml

31ml

Final volume of water in CO2 collecting cylinder"

19ml

11.5ml

12ml

Volume of CO2 collected

19ml

19.5ml

19ml

Temperature of water

25oC

Barometric pressure

763.7 torr

Vapor pressure of H2O at 25oC

23.8 torr

Pressure of "dry" CO2

739.9 torr

                                                                                                                                              Godoy 5

Table #3: Mass of Carbon Dioxide Evolved

Trial 1

Trial 2

Trial 3

Mass of generator + sample after reaction

167.41g

167.14g

166.73g

Mass loss of generator = mass CO2 evolved

0.21g

0.44g

0.74g


Table #4: Molar Volume  of CO2 Gas

Trial 1

Trial 2

Trial 3

Pressure of "dry" CO2

0.97atm

Volume of CO2 at STP

0.0168L

0.0173L

0.0168L

Moles of CO2 generated

6.6x10-4mol

6.8x10-4mol

6.6x10-4mol

Molar volume of CO2 at STP

25.45L/mol

25.44L/mol

25.45L/mol

Average volume of CO2 at STP

25.44L/mol

Table #5: Percent CaCO3 in mixture

Trial 1

Trial 2

Trial 3

Moles of CaCO3 in sample

6.6x10-4mol

6.8x10-4mol

6.6x10-4mol

Mass of CaCO3 in sample

0.066g

0.068g

0.066g

Mass of original sample

0.083g

0.082g

0.083g

Percent of CaCO3 in sample

79.50%

82.90%

79.50%

Average percent of CaCO3 in sample

80.60%

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

                                                                                                                                        Godoy 6

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

                                                                                                                                        Godoy 7

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.

                                                                                                                                              Godoy 8

        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.

                                                                                                                                              Godoy 9

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.

                                                                                                                                  Godoy 10

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.

                                                                                                                                      Godoy 11

  1. 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.

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