Science Brain NEEDED!!!?

Question

compute the weight of 3.5 cu ftof air at a pressure of 40 psia and at 120.4F.?

A) 0.0045LB

B) 0.65LB

C) 1.23LB

D) 3.14LB

Can you show me how you got it? thanks!!!!

Answer 1

Answer is B

PV = nRT   or  PV =  (m/M)RT   or   m = (PVM) / RT

Where P = atmospheric pressure in atmospheres

             V = volume of the air in L

             M = average molar mass of air,  29.0 g/mol

             R = air gas constant,  0.083 L∙ atm/k ∙ mol  

             T =  temperature in Kelvin

            m =  mass of the air in g

You will have to make a whole lot of conversions:

cu. ft. to Liters

psia to atm

degrees F to degrees K

grams to lbs.

The rest is just plug and chug.

Answer 2

use PV=nRT n= mole of air ==> n=m/M, m=mass of air , M= molar mass of gas , P= pressure , V=volume , R= gas constant = 8.31 , T=temperature

In S.I. unit like metre^3, pascal, mole, Kg