# 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

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### 1 Answer

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 :)