What is the pressure?

Question

Some of the best laboratory vacuum systems can pump down to as few as 1.0 109 molecules per cubic meter of gas. Calculate the corresponding pressure, in atmospheres, assuming a temperature of 25°C.
____________atm

Answer 1

you have pV=nRT

calculate the number of moles T=25+273=298, V=1m^3

1 mole = 6.023 *10^23 molecules
n= 10^9/6.023*10^23=1.66*10^-15 mole

p = nRT/V =1.66*10^-15*8.31*298 =4.11-10^-12 pa