Molar Mass

[Awuah29]

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heh guys,
have a molar mass problem coming from kaplan
What is the molar mass of 2 Liter sample of gas that weights 8g at a temp. of 15C and 1.5 atm.
I used this formula to solve : molar mass = dRT/ P
however I don't get the answer that kaplan came up with 63.,2 g/mol
help needed,
thanks

 

[duh?]

played around with the numbers and i came up with this. I do not trust my answer cos i did it 2ce and came up with this and another value that was half of 62.99 g/mol. Maybe someone who is sure can explain better. here goes:
molar mass (g/mol) = Mass Concentration (g/L) / Molar Concentration (mol/L)
Mass Conc= 8g/2L= 4g/L
Using PV=nRT
n= (1.5*2)/ 0.08205*288K
n=0.127mole
The 8g gas has 0.127 mole of substance in 2L
in 1L it would have 0.0635mole/L
When we plug in the numbers Molar mass= 4(g/L)/0.0635(mole/L)= 62.99g/mol

 

[g3k]

To the above poster: Your answer is correct .. just that if you follow significant figures and carry the digits until the last step the answer is 63.2. That is the reason for difference.

 

[Awuah29]

played around with the numbers and i came up with this. I do not trust my answer cos i did it 2ce and came up with this and another value that was half of 62.99 g/mol. Maybe someone who is sure can explain better. here goes:
molar mass (g/mol) = Mass Concentration (g/L) / Molar Concentration (mol/L)
Mass Conc= 8g/2L= 4g/L
Using PV=nRT
n= (1.5*2)/ 0.08205*288K
n=0.127mole
The 8g gas has 0.127 mole of substance in 2L
in 1L it would have 0.0635mole/L
When we plug in the numbers Molar mass= 4(g/L)/0.0635(mole/L)= 62.99g/mol

Kaplan, has this problem set up differently. Are there any other ways to approach this problem diffrently???

 

[786mine]

To the above poster: Your answer is correct .. just that if you follow significant figures and carry the digits until the last step the answer is 63.2. That is the reason for difference.

i concure. i did using the same formula myself.

 

[GENERAL TSO]

heh guys,
have a molar mass problem coming from kaplan
What is the molar mass of 2 Liter sample of gas that weights 8g at a temp. of 15C and 1.5 atm.
I used this formula to solve : molar mass = dRT/ P
however I don't get the answer that kaplan came up with 63.,2 g/mol
help needed,
thanks

whats crazy is that you prob wont see anything like that on the DAT.

As you know they dont give you calculators to use so theres no way they can expect a bunch of those questions.