Coleman Powermax fuel is a liquid fuel for camp stoves. Before this product was discontinued, it was sold in aluminium canisters. The liquid contents — under
pressure — are claimed to consist of
35% (m/m) propane (C3H8, boiling point –42 oC) and
65% (m/m) butane (C4H10, boiling point –1 oC).
In an attempt to verify the proportions (m/m) of this fuel, the following experiment was performed: the canister was cooled with saturated NH4Cl(aq) and lots of ice. Working in a fume hood, the chemists punctured the canister with a hammer and a nail.
This caused some gas to be emitted from the puncture hole. This emission of gas continued for ca 30 seconds. Then the remaining material in the canister — a clear liquid — was poured into a clear 2-L pop bottle and was allowed to boil away, leaving the pop bottle full of the gas form of the material; the bottle was then capped.
Questions
- Why was the canister cooled prior to being punctured? Why was the canister cooled in a bath of ice and NH4Cl(aq) instead of just plain ol’ ice and water?
- Use the data above to determine the average molar mass of the gas collected.
- How does your answer compare with the manufacturer’s claim with respect to the 35% (m/m) propane and 65% (m/m) butane? Provide a reasonable explanation for your answer. Provide a new data point for “pop bottle containing Coleman Powermax gas + lid” to support the gas mix claimed by the manufacturer.
| “empty” soda bottle (contains air) + lid | 45.288 g |
| volume of soda bottle | 2.10 L |
| air pressure in the lab during the experiment | 763.3 mmHg |
| temperature of room during the experiment | 23.4 oC |
| soda bottle containing Coleman Powermax gas + lid | 47.819 g |
| mass of full Powermax cylinder before the experiment (with C3H8/C4H10 gas mixture) | 226.92 g |
| mass of empty Powermax cylinder after experiment | 83.25 g |
| approximation of components of air (v/v) | 78% N2, 21% O2, 1% Ar |
Teacher’s note: Please note this is just the general outline of the procedure and details of the safety precautions are not listed. This data give an answer of almost 100% butane. Most of the propane "disappeared" as a gas when the cylinder was punctured. Careful reading of the up-front material reveals this clue. Email Jean Hein for a complete solution; jhein@uwaterloo.ca.
