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Molar mass, atm, pressure, find mass. HELP

by teggenspiller
Tags: kinetic energy, nitrogen, thermodynamics
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teggenspiller
#1
Jun8-11, 12:30 PM
P: 94
1. The problem statement, all variables and given/known data

A nitrogen in the container (molar mass is 28 g/mol) has a pressure of 2.5 atm, a volume of 0.2 m3, and a temperature of 300C. What is the mass of the nitrogen?

2. Relevant equations

first figure how many
moles there are

n=PV/RT

however, i need to use Pressure, Pa, and not in atmospheres.
3. The attempt at a solution
how do i figure the pressure in Pa, and not atm. or can I use atm?
hmmmm
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gneill
#2
Jun8-11, 01:22 PM
Mentor
P: 11,683
Google: 1 atm in Pascals
teggenspiller
#3
Jun8-11, 01:25 PM
P: 94
i did its 101.3 or 103.1. but either way i couldnt come up with correct answer... :( can u show me how to solve this.. ?

teggenspiller
#4
Jun8-11, 01:28 PM
P: 94
Molar mass, atm, pressure, find mass. HELP

VP/RT
.2*253312.5/(8.31*303)= # of moles,
multiplied by 28 grams per mole

*(28)
563.37944
gneill
#5
Jun8-11, 01:32 PM
Mentor
P: 11,683
Quote Quote by teggenspiller View Post
i did its 101.3 or 103.1. but either way i couldnt come up with correct answer... :( can u show me how to solve this.. ?
Your methodology looked okay to me. Try again, posting your calculations step by step.

Notes:
1. 1 atm = 101,325 pascals or 101.3 kPa
2. Make sure that your temperature is absolute (Kelvin).
teggenspiller
#6
Jun8-11, 01:35 PM
P: 94
okay thank you. one minute.
teggenspiller
#7
Jun8-11, 01:40 PM
P: 94
P= (253312.5) Pa
R=8.31 J/(mol K)
V= in Liters of m^3??
V= .2m^3 or 200Liters
T= 273.15+30 = 303.15

(253312.5) * ( .2) / (8.31J/(mol K) *(303.15)=
1848175.32


*28g/mol

=51748908.8

much too big
gneill
#8
Jun8-11, 01:49 PM
Mentor
P: 11,683
I thought that your temperature was 300C? You've used 30

The formula is n = p*v/(R*T) ; you have to divide by temperature, not multiply!
teggenspiller
#9
Jun8-11, 01:50 PM
P: 94
ha okay
teggenspiller
#10
Jun8-11, 01:50 PM
P: 94
jeez i completely missed that. thnaks!
teggenspiller
#11
Jun8-11, 02:18 PM
P: 94
i still am not geting the right thing? do i times the final answer by the grams/mol (28//)
gneill
#12
Jun8-11, 02:20 PM
Mentor
P: 11,683
Quote Quote by teggenspiller View Post
i still am not geting the right thing? do i times the final answer by the grams/mol (28//)
Yup. You should by now have n (from PV = nRT), and that's the number of moles. So number of moles multiplied by grams/mole will yield grams.
teggenspiller
#13
Jun8-11, 02:32 PM
P: 94
A. 125 g
B. 258 g
C. 421 g
D. 582 g
E. 864 g
gneill
#14
Jun8-11, 02:56 PM
Mentor
P: 11,683
Quote Quote by teggenspiller View Post
A. 125 g
B. 258 g
C. 421 g
D. 582 g
E. 864 g
I take it that these are the choices for answers to the question? If so, it looks to me like the correct answer corresponding to the initial values given in the problem statement is not in the list.

What final value for the grams of N2 did you calculate?

Is it possible that the starting values were modified to 'present a new problem'?


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