A 9.1 gram sample of gaseous substance occupies 15 L at 23C and 785 torr. What is the density of the gas at STP? Answer in units of g/L

Expert Answers
jerichorayel eNotes educator| Certified Educator

Hello! 

We can answer this proble by using the ideal gas equation, 

PV = nRT.

First we have to get the number of molecular weight of the substance using the first condition of the gas. 

PV = nRT    n = mass/molecular weight  = M/MW

PV = MRT/ MW

Given:

M = 9.1 g

R = 0.08206 atm-L/mole-K

T = 23 + 273.15 = 296.15 K

P = 785/760 = 1.0329 atm

V = 15L

 

MW = MRT/PV

      = (9.1g)(0.08206atm-L/mole-K) (296.15K)/(1.0329atm)(15L)

      =14.2737 g/mole

 

Now we can get the density of the subtance at STP.

At STP, T = 273.15, P = 1atm.

density= P MW/ RT

       = (1atm)(14.2737 g/mole)/(0.08206atm-L/mole-K)(273.15K)

  density  = 0.6368 g/L = 0.64 g/L



Hope this helps :)