Chem

[211183]

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Sorry for so many questions lately... working on my weakest stuff today.

What is the molar mass of a 2L sample of gas that weighs 8g at T of 15*C adn a pressure of 1.5 atm?

The Kaplan book sets it up...


2L (273K/288K)*(1.5/1atm)

then

8g/ 2.84 L = 2.82 g/ L

then just go to g / mol by multiplying by 22.4


This is quite confusing to me... is there a more intuitive wayt o do it?
I set it up...

OPPosite

2L (288/273) (1/1.5)

I thought since you are increasing V you need to decrease P and increase T

Am I missing something? The book teaches it the way I did it just before, and this problem flips it. If somoen can just explain how that works. Am I thinking too much?

 

[Chesnok]

just memorize formula for MM/density --it saves time IMO.

 

[211183]

what about the reset of hte info? how does memorizing that help in this prob?😕

 

[iverson3504]

alright here's the intuitive way of doing this problem:

pv=nrt or pv=(m/mw)rt

solve for mw

mw= (mrt)/(pv)

(8*.0821*288)/(1.5*2)

=63 g/mol

 

[klpennin]

alright here's the intuitive way of doing this problem:

pv=nrt or pv=(m/mw)rt

solve for mw

mw= (mrt)/(pv)

(8*.0821*288)/(1.5*2)

=63 g/mol

Just as iverson said, remember n(moles)= g of sample/molar mass, so you have everything but mm, which is what you are looking for...

 

[Contach]

maybe you are missing the formula they used
P1V1/T1 = P2V2/T2
if you plug in numbers, you can't really go wrong...

 

[hoyas19]

P(Molar Mass) = Density (R)(T in kelvin)
is another form of PV=nRT..really helpful to know both

(also very similar to osmotic pressure = iMRT)


you have grams and liters to find density, so just plug in the other numbers and solve for molar mass.

 

[211183]

maybe you are missing the formula they used
P1V1/T1 = P2V2/T2
if you plug in numbers, you can't really go wrong...

that is what i thought but it doesnt work... tehy did everything flipped the opp way..im pretty sure

 

[211183]

P(Molar Mass) = Density (R)(T in kelvin)
is another form of PV=nRT..really helpful to know both

(also very similar to osmotic pressure = iMRT)


you have grams and liters to find density, so just plug in the other numbers and solve for molar mass.

Is that

PM=DRT if you just put letters

m = m/MM
D=g/L

 

[211183]

sorry couldn't get it to edit. the answer is 63.2 g/mol... not getting that..

 

[211183]

alright here's the intuitive way of doing this problem:

pv=nrt or pv=(m/mw)rt

solve for mw

mw= (mrt)/(pv)

(8*.0821*288)/(1.5*2)

=63 g/mol

end post. sorry for bringin this to the top so many times. I got understand. I guess I was making it to complex. thanks iverson.