Please answer the questions 11. Based on your answer to question #9 above, which
ID: 859183 • Letter: P
Question
Please answer the questions
11. Based on your answer to question #9 above, which other hydrocarbons listed below could be mixed with butane to give the average molar mass you determined? POST-LABORATORY QUESTIONS 1. Except for very small alkanes (hydrocarbons), the boiling point rises 20-30 degrees for each additional carbon atom in the molecule. Assume that the normal boiling point of the fuel in the lighter is 10 degree C, why was it not necessary to extend the table further (i.e., why was it unlikely that your unknown contained more than eight carbon atoms per molecule)? 2. A gaseous hydrocarbon collected over water at a temperature of 21 degree C and a barometric pressure of 753 torn occupied a volume of 48.1 mL. The hydrocarbon in this volume weighs 0.1133 g. Calculate the molecular mass of the hydrocarbon. 3. How is the ideal gas law related to the molar mass of a gas?Explanation / Answer
1.
If the boiling point of alkanes in a lighter exceeds room temperature, then they will not spontaneously vaporize when you open the aperture of the lighter to ignite the gas.
Start from the boiling point of methane (CH4) and add +20-30 deg C for each carbon added: ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, and all their isomers.
What temp do you reach in the boiling point with the theoretical increase of 20-30 deg C for each carbon added, and when you go from octane (8 carbons) to nonane (9 carbons)? Does the boiling point pass what is typical room temperature (20-25 deg C)
2.
T=21+273=294 K
P=753/760=0.991 atm
V=48.1*10^-3=0.0481 L
PV=nRT so;
n=PV/RT=0.991*0.0481/(0.0821*294)=1.97 * 10^-3 mol
M=m/n=0.1133/0.00197=57.5 g/mol
so its formula is C4H10 & the correct MW=58 g/mol. This difference in answer is because of the experiment error.