DATA COLLECTION & PROCESSING (DCP)
RAW DATA –
*Volumes were taken from the top end of the beaker because the beaker was turned upside-down
PROCESSING RAW DATA –
mi = initial mass of lighter mf = final mass of lighter ∆m = mass of butane
Pressure of Butane:
30.02 inHg (25.4 mmHg / 1 inHg) (1 atm / 760 mmHg) = (20.45 mmHg x (1atm / 760 mmHg)) + Pressure of Butane
Pressure of Butane = 0.976 atm
n = PV/RT (Trial 1)
n = (0.976 atm)(0.0134 L) / (0.08206 Latm/molK)(295.65)
n = 5.39e-4
n= PV/RT (Trial 2)
n = (0.976 atm)(0.0143 L) / (0.08206 Latm/molK)(295.65)
n = 5.75e-4
n= PV/RT (Trial 3)
n = (0.976 atm)(0.0158 L) / (0.08206 Latm/molK)(295.65)
n = 6.356e-4
n= PV/RT (using averages)
n = (0.976 atm)(0.0145 L) / (0.08206 Latm/molK)(295.65)
n= 5.833e-4
Percent Error:
The accepted value of the molar mass of butane is 58.124 g/mol. To calculate percent error:
Trial 1: Difference between Calculated and Accepted values = 58.124 g/mol – 55.65 g/mol = 2.474 g/mol
Trial 2: Difference between Calculated and Accepted values =58.124 g/mol – 69.53 g/mol =
-11.406 g/mol
Trial 3: Difference between Calculated and Accepted values = 58.124 g/mol – 47.20 g/mol = 10.924 g/mol
Average: Difference between Calculated and Accepted values = 58.124g/mol – 56.57g/mol = 1.554g/mol
CONCLUSION AND EVALUATIONS (CE)
CONCLUDING –
Determining the molar mass of butane through experimentation is possible with multiple trials. The more trials completed, the closer the average molar mass of butane is to the accepted value of the molar mass of butane. To determine the molar mass, take the mass of butane in the beaker and divide that by the number of moles of butane. Then determine the pressure of butane, volume of displaced water, and temperature of the water/butane gas. Once pressure, moles, volume, and temperature have been determined, plug the values into the ideal gas law equation, PV=nrT, to determine moles. Molar mass is grams / moles, so take the mass / moles. The accepted value of molar mass of butane is 58.124 g/mol, and our average calculated value of the mass of butane is 56.57g/mol.
EVALUATING THE PROCESURE(S) –
A random error is caused by variability in samples. It can vary between trials of an experiment, and it commonly defined as the deviation from the true accepted value. A random error can be solved by repetition of the experiment. A random error that occurred in this lab is that when the lighter was put under water to release butane into the beaker, water went into the lighter. When the lighter was weighed for the next trial, the weight was slightly off due to the existing water inside the lighter. A systematic error is an error caused by a variation in samples. Systematic errors usually occur from faulty equipment. Repetition does not solve systematic errors, and the value is referred to as a bias or the deviation from the true value. A possible systematic error that may have occurred in this lab is that the butane from the lighter may have contained air or a substance other than butane in the lighter, skewing the measured amount of butane gas collected at the top of the beaker. Another systematic error was that if the beaker was even slightly cracked at the top, allowing air to enter the beaker, the value of molar mass would change because the gas collected at the top of the beaker would no longer be strictly butane. Another systematic error that could have occurred is that the ambient room pressure was taken from a website dictating the pressure in the area, rather than directly in our room. The measurements in the lab are reliable taking into consideration the equipment windows of error and there are few to no flaws and weaknesses in the procedure itself.
IMPROVING THE INVESTIGATION –
The experiment could have been improved by measure the atmospheric pressure directly in the room, obtaining a more accurate room pressure to ensure that the pressure of butane was calculated correctly. Other improvements may include more accurate equipment such as a balance, beaker, and thermometer. Also, the butane used in the experiment could have been certified as pure butane, rather than butane from a common lighter.
APPENDICES –
"Cornellbiochem - Butane." Cornellbiochem - home. Web. 08 Nov. 2009.
Brown, Theodore L., H. Eugene LeMay Jr., Bruce E. Bursten, and Catherine J. Murphy. Chemistry The
Central Science; AP Edition. 10th ed. Upper Saddle River: Prentice Hall College Div, 2005. Print.
