Answer
0.173 g
Work Step by Step
$P=626\, mmHg\times\frac{1\,atm}{760\, mmHg}=0.8237\,atm$
$V=355\,mL=0.355 L$
$R=0.0821\,L\,atmmol^{-1}K^{-1}$
$T=(35+273)K=308\,K$
$PV= nRT$ (ideal gas law)
$\implies n= \frac{PV}{RT}=\frac{0.8237\,atm\times0.355\,L}{(0.0821\,L\,atm\,mol^{-1}K^{-1})(308\,K)}$
$=0.01156\,mol$
But $n(total)= n(Ne)+n(Ar)$
$n(Ne)=\frac{mass\, of\,Ne}{molar\,mass\,of\,Ne}$
$=\frac{0.146\,g}{20.1797\,g/mol}=0.007235\,mol$
$n(Ar)=n(total)-n(Ne)$
$=0.01156\,mol-0.007235\,mol$
$=0.004325\,mol$
Mass of Ar= $n(Ar)\times molar\,mass\,of\,Ar$
$=0.004325\,mol\times 39.948\,g/mol$
$=0.173\,g$
