Gchem Question

[Predentole]

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what is the molar mass of a 2L sample of gas that weighs 8g at a temperature of 15C and a pressure of 1.5 atm??
can someone show me how to work this and will questions on the DAT be this hard?

 

[TeamGuo]

what is the molar mass of a 2L sample of gas that weighs 8g at a temperature of 15C and a pressure of 1.5 atm??
can someone show me how to work this and will questions on the DAT be this hard?

You just have to use the ideal gas law equation with a little modification.

PV = nRT

PV = (mass/MM) RT
Rearramge.

MM = mass (RT/PV)

Plug and chug question, very fair for the DAT.

 

[Predentole]

You just have to use the ideal gas law equation with a little modification.

PV = nRT

PV = (mass/MM) RT
Rearramge.

MM = mass (RT/PV)

Plug and chug question, very fair for the DAT.

i wish that was true but Kaplan does some weird set of equations i never seen in my life.

density = 8g/2L at 15C and 1.5 atm

Vstp = (2L) x (273K/288K) x (1.5atm/1atm) = 2.84L

8g/2.84L = 2.82 g/L at STP

(2.82g/L) x (22.4L) = 63.2g/mol

 

[DRHOYA]

This is based off of PV=nRT. And also D=M/V. Now based on those two equations, you can re-write the ideal-gas-law to conform to your question. So P(MW) = DRT. This is a good equation to memorize along with the ideal-gas-law. MW = molecular weight, and D = density. I just use the nmenoic as "p-molecular weight = dirt". Hope that helps man.

 

[TeamGuo]

i wish that was true but Kaplan does some weird set of equations i never seen in my life.

density = 8g/2L at 15C and 1.5 atm

Vstp = (2L) x (273K/288K) x (1.5atm/1atm) = 2.84L

8g/2.84L = 2.82 g/L at STP

(2.82g/L) x (22.4L) = 63.2g/mol

Yes, kaplan's equation is same thing. You'll get used to this rearrangement with some more practice. Whenver you approach ideal gas related problem, think about different ways to rearrange the PV=nRT formula.