CHM 1025C Module Six Sample Exam ANSWERS    

 

Module Six Part H-1 Gas Density Problem                   10 points

 

Calculate the gas density of octane gas C8H18 vapor at STP?

First: find the volume of gas:  1.00 mole C8H18  = 22.4 L@STP by definition

 

Second: what is the Mass of 1 Mole of C8H18 :

 

8 carbons @ 12.0 =    96.0 g carbon atoms

18 hydrogens@ 1.0 = 18.0 g hydrogen atoms

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          1 mole C8H18  =    114.0 g C8H18

 

Third: Find the density of octane:

 

Density @STP = mass/volume  = 114.0 g C8H18 / 22.4 L@STP = 5.09 g/L@STP

 

Answer = 5.09 g/L@STP

 

 

 

 

Calculate the gas density of octane gas C8H18  at 27 oC and 750 torre?.

 

First:  Change the pressure to atmospheres:
             750 torre/760 torre =  0.987 atm

 

           Change the Temperature to Kelvin:

              27oC + 273 =  300 K

 

           Calculate the volume of 1 Liter @ STP at 27 oC and 750 torre:

 

            V2 = (V1P1T2)/(T1P2)

 

            V2 = [(1.00 L) (1 atm) (300K)] / [(273 K) (0.987 atm)]

 

          V2 = 1.11 L

          

Second:  Calculate the density of 1.11 L at 27 oC and 0.987 atm which weighs 5.09 grams:

 

Density @27oC and 0.987 atm = mass/volume =  5.09 g / 1.11 L = 4.59 g/L

 

Answer = 4.59 g/L@27oC and 0.987 atm