Purpose
In this experiment we will determine the molecular weight of the gas used in our lab Bunsen burners.  We will do this by comparing the mass of a known volume of burner gas to the mass of an identical volume of air under the same conditions.

Pre-Lab
The molecular weight of air is the weighted average of the molecular weights of the gases that make up air.  Look up the composition of dry air.  Ignoring water, and gases present only in trace amounts, determine the molecular weight of dry air.

Look up and read Avogadro's Hypothesis.  Look up and read the definiation of "buoyancy."

Discuss with your lab partner(s) what information you would need to determine the molecular weight of burner gas.  How could you measure this information?

Procedure: Mass of A Gas

1. OK, now get this information, and determine the molecular weight of burner gas.
2. Decide whether the burner gas is most likely CH₄, C₂H₆, or C₃H₈.  Explain the basis for your decision.
3. The gas in the burner is actually a mixture of two of the gases listed above.  There are three possible pair combinations.  Given the calculated molecular weight, what is the percentage of each gas in each possible mixture?

• A heading that includes your name, your partner’s name, the date, and the title of the lab.
• A data table that includes every measured quantity.  Remember that every value should be described in English AND labeled with the proper units (for example,  Mass of Cheeseburger  118.2 g )
• A calculations/results section that describes and clearly shows every calculation.  Make sure I know what you are thinking.
• A decision about which formula most likely applies to the burner gas.
• A decision about which combination of gases is most likely.
• A discussion that includes any opinion about the lab or results, any possible errors, and any suggestions for getting better results.