Molar Mass Of Butane Chemistry Lab printable pdf download

Molar mass of Butane LAB.doc

MOLAR MASS OF A GAS DETERMINED EXPERIMENTALLY

PRE-LAB DISCUSSION:

In this lab, we are going to determine the molar mass of butane, C

, experimentally. A simple

calculation using a periodic table would give us the correct answer for the molar mass of butane,

however, you are going to conduct an experiment in the lab to see how close you can come to

the accepted value. From Section 14.3 in the book, we know that PV = nRT. The ideal gas law

equation can be rearranged to solve for n, the number of moles:

n = PV

We are trying to find the molar mass, which is expressed in units of grams per mole (g/mol). We

will measure the mass of the butane released from the pressurized container, and we will

measure the volume of the gas that we collect. You can use the method of water displacement at

room conditions and then substitute the measurements of volume, temperature, and pressure into

the ideal gas law equation in order to find n, the number of moles of butane. Once we know the

mass, and the number of moles, we will divide the mass by the number of moles to calculate the

molar mass (g/mol).

WARNING: Butane is a flammable gas, and at NO TIME during this lab should there be

any use of an open flame or other heat source!

QUESTION: What is the molar mass of butane? Butane is the gas used as fuel for a cigarette

lighter.

HYPOTHESIS: If we can capture a sample of gas and determine the mass of the sample and the

number of moles, then we can calculate the molar mass using the following equation:

Molar Mass = mass of sample in grams

number of moles

PROCEDURE:

1. Determine the initial mass for the butane lighter provided by your instructor ( +/- .01 gram ).

2. Set up the water basin for collecting a gas in an inverted graduated cylinder by water

displacement. Use a 100 mL graduated cylinder.

3. Release butane from the pressurized container and collect a sample of gas with a volume of

approximately 70.0 mL to 90.0 mL. Collect every bubble that leaves the lighter. If you

miss a bubble, you will have to repeat the entire procedure beginning with re-weighing the

clean and dry lighter.

4. Adjust the cylinder up or down so that the water level inside the graduated cylinder is the same

as the level outside the cylinder. THIS IS VERY IMPORTANT! If you miss this simple step,

the pressures inside and outside the cylinder will not be equal, and you will have an

inaccurate estimation of the pressure inside the cylinder where the gas is collected.

5. Record the volume of butane that was collected in the Observations and Data section.

6. Measure and record the temperature of the water in the basin ( +/- 0.1 °C ). This will be used

to determine the vapor pressure of water H

in the graduated cylinder.

(g)

(a Table of water vapor pressure at a given temperature is on the back)

7. Read the barometric pressure in the lab (inches of Hg ) and convert this to mm Hg (using the

conversion factor 1 inch Hg = 25.4 mm Hg) and then to kPa.

8. Make sure the lighter is dry then, measure and record the mass of it ( +/- .01 gram).

9. Clean and return all materials to the starting position for the next class.

10. Report your measurements and calculations on the class data sheet.

Molar Mass Of Butane Chemistry Lab

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