Answer :
Answer
[tex]P=8.3360\times10^{-3}\text{ }Torr[/tex]Procedure
The gas can be considered ideal given the temperature conditions. Therefore we can use the ideal gas formula
[tex]PV=nRT[/tex]Before substituting the values we need the moles of oxygen
[tex]2.1\times10^{-6}g\text{ }O_2\frac{1mole\text{ }O_2}{31.999g\text{ }O_2}=6.56\times10^{-8}\text{ }mole\text{ }O_2[/tex]Then we need the gas constant that contains Torr as pressure units
R=62.363577 L.Torr.°K⁻¹.mol⁻¹
We need to convert the volume and temperature into the constant units
T= 12°C+273.15=285.15°K
V=140mL=0.140L
Now we can proceed to substitute the values in the ideal gas equation
[tex]P=\frac{nRT}{V}=\frac{(6.56\times10^{-8})\text{ }mol\text{ }(62.36)L.Torr.\degree K^{-1}.mol^{-1}(285.15)\degree K}{(0.140)\text{ }L}[/tex][tex]P=8.3360\times10^{-3}\text{ }Torr[/tex]