Except for very small alkanes (hydrocarbons), (he boiling point rises 20-30 degr
ID: 930078 • Letter: E
Question
Except for very small alkanes (hydrocarbons), (he 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)? A gaseous hydrocarbon collected over water at a temperature of 21 degree C and a barometric pressure 753 torr occupied a volume of 48.1 mL. The hydrocarbon in this volume weighs 0.1133 g. Calculate the molecular mass of the hydrocarbon. How is the ideal gas law related to the molar mass of a gas?Explanation / Answer
1. As the boiing point changes, the state of the subsance also changes. For example, as the boiling point increases, the substance becomes a solid at room temperature. Hence, it can't be extended.
2.from PV= nRT PV= (mass/ molecular weight)*RT
Given P= 753 torr =753/760 atm=0.9907
T= 21deg.c =21+273.15 =294.15 K V= 48.1 ml =48.1/1000 =0.0481 L R =0.08206 L.atm/mole.K
0.9907*0.0481 = 0.1138* 0.08206* 294.15/ molecular weight
Molecular weight= 0.1138 *0.0820*294.15/ (0.9907*0.0481) =57.6 g/mole
3. PV= nRT n= mass/ molar mass
PV= (mass/ molar mass)*RT
Molar mass = mass*T*R/PV
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