Question

Forty miles above the earth's surface the temperature is 250 K and the pressure is only 0.20 mm Hg. What is the density of air (in grams per liter) at this altitude? (Assume the molar mass of air is 28.96 g/mol.)

PV=nRT
n/V= molar desity= P/RT
mass density= molar density*molmass
= P*(molmass)/RT

Watch your units.

Answer 1

0.20 mm Hg = 0.20*133.322 Pa

mass density= (0.20*133.322*28.96)/(8.314*250)

= 0.0014 g/L