Calculate Mass of Nitrogen in 2.5 atm, 0.2 m3, 300C

[teggenspiller]

Homework Statement

. 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?

A. 125 g
B. 258 g
C. 421 g
D. 582 g
E. 864 g

Homework Equations

I'll show you EXACTLY what i am doing:

The Attempt at a Solution

so first i must find moles, since moles times molar mass = the mass. (is that correct??)

so n(moles)= PV/RT (

P=2.5 atm = 101325*2.5= 253312.5
V= .2 m^3
R= 0.0821 a constant
T= 300C = 573.15K

so 253312.5 * .2 / 0.0821 * 573.15 = moles

= 50662.5/ 47.1

=1075.63 = moles

the molar mass is 28g/mol
so 1075.63 * 28 grams=
30117.6

not an answer.

i have no idea what i am doing wrong, this whole class is finished today. i really need some help and an idea of what exactly i am doing wrong.

 

[gneill]

R is 8.314 J/mol/K, so your number of moles calculated is too large.

 

[teggenspiller]

i was about to post that R= 8.315 J/mol.K , and the entire time (til just now) I've been using R= 8.315 J/mol.K ) but i thought id try soemthing else,
so with either R i haven't been able to come up with anything. i mea, if you solve it are you getting a correct answeR? is it working for you and maybe my calculations are off? or have i input something wrong. when i use R=8.315 J/mol.K i keep gettin 297 grams.

 

[gneill]

i was about to post that R= 8.315 J/mol.K , and the entire time (til just now) I've been using R= 8.315 J/mol.K ) but i thought id try soemthing else,
so with either R i haven't been able to come up with anything. i mea, if you solve it are you getting a correct answeR? is it working for you and maybe my calculations are off? or have i input something wrong. when i use R=8.315 J/mol.K i keep gettin 297 grams.

I see 297.7 grams for the mass. Is that not correct? If it is not, then perhaps the pressure is gauge pressure and not absolute pressure? Did the problem specify?

 

[teggenspiller]

oh yes perhaps. let me see...
so gauge pressure means 1atm+2.5 atm= 354637.5

*.2 = 70927.5
/ (8.31*573.15) = 14.89Do you think i should contact my teacher? perhaps maybe the solutionn isn't an option?

 

[gneill]

oh yes perhaps. let me see...
so gauge pressure means 1atm+2.5 atm= 354637.5

*.2 = 70927.5
/ (8.31*573.15) = 14.89


Do you think i should contact my teacher? perhaps maybe the solutionn isn't an option?

Well, as I said, assuming that the given pressure is absolute pressure, I calculated about 298 grams for the mass.

I notice that the value for the volume is given to only one significant figure. Perhaps the answer needs to be specified with a corresponding accuracy: 300 grams.

 

[teggenspiller]

not an answer. either.

 

[teggenspiller]

or perhaps the molar mass of nitrogen is wrong? i searched google and see that 14.01g/mol is molarmass of nitrogen..

 

[gneill]

or perhaps the molar mass of nitrogen is wrong? i searched google and see that 14.01g/mol is molarmass of nitrogen..

That's for monatimic Nitrogen, N. Nitrogen gas is N₂, twice that.

 

[teggenspiller]

bummer. I think i might just have to guess on this one.

 

[Borek]

298 g no matter how you try. Even assuming 3.5 atm (2.5 + 1) or 300 K (possible typo) neither of the answers given fits.