Question

A flask containing $12 g$ of a gas relative molecular mass $120 at$ a pressure of $100 atm$ was evacuated by means of a pump until the pressure was $0.01 atm$. Which of the following in the best estimate of the number of molecules left in the flask $(N_(0)=6xx10^(23)mol^(-1))$?
A. $6xx10^(9)$
B. $6xx10^(18)$
C. $6xx10^(17)$
D. $6xx10^(13)$

Answer 1

$P(1)V(1)=n(1)RT(1)$
$P(2)V(2)=n(2)RT(2)$
$(n(2))/(n(1))=(P(2))/(P(1))$
$n_(2)=0.1xx(0.01)/(100)=10^(-5) mol= 6xx10^(18)$ molecules