Question

What is the molar quantity of a gas at `742*mm*Hg` pressure, at `298.0*K` temperature, confined to a volume of `6.0*L`?

Answer 1

`n=0.240*mol`

Explanation:

We use the old ideal gas equation, i.e. `PV=nRT`

`n=(PV)/(RT)=((742*cancel(mm*Hg))/(760*cancel(mm*Hg*atm^-1))xx6.0*cancelL)/(0.0821*cancel(L*atm*K^-1)*mol^-1xx298.0*cancelK)`

`=0.240*mol`

What mass of `HC-=N` is present? Would you expect `HC-=N` to behave ideally? Why or why not? What hazards would be associated with this experiment?

Note the dimensional consistency of our calculation. We sought an answer in `"moles"`; the calculation gave us an answer in `"moles"` or at least `1/(mol^-1)=1/(1/(mol))=mol`, so perhaps we are doing something right (for once!).

The key knowledge is the idea that `1*atm` will support a column of mercury that is `760*mm` high. And thus we may use a unit of length, the height of a mercury column, to give a useful and reproducible measurement of pressure.

Note that these days, mercury columns are a bit of a rarity. Has your teacher shown you a mercury column?