Butane Molar Mass Lab Essay


Butane is a colorless gas with the molecular formula of C6H10 and is considered to be an Alkane. An Alkane is when the compound is formed by single bonds connecting the carbons and hydrogens. Butane was discovered by Dr. Walter Snellings in Pittsburg and he gas is used for cigarette lighters, heaters, stove fuels, and other heating appliances. The accepted value for the molar mass of butane is 58.124 g/mol.

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We tested the accepted value by calculating the molar mass of butane in a butane cigarette lighter.

We took a beaker, and submerged it into water. Then we measured the mass of the cigarette lighter, and then slowly released butane gas bubbles into the beaker so that the bubbles collected at the top, where there was no air. We recorded the initial volume of water, then equalized the pressure inside and outside the beaker until the water levels inside and outside the beaker were the same. Then we recorded the final volume of water, and repeated the experiment until we had three trials.

We concluded that the molar mass of butane can be determined through the average of repeated trials of the experiment were no systematic or random errors occur.



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.


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.


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.


“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.

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