Question

My textbook says that that for a mixture of `15.2*g` helium gas, and `30.6*g` dioxygen gas, the partial pressure is dominated by the helium. Can you find `P_"He"`, and `P_"dioxygen"` and `P_"Total"`?

Answer 1

Well, I think the text book is right mate. Because `"helium gas"` is present in a large molar quantity, its partial pressure should dominate. Let's see what we get.

Explanation:

`"Dalton's Law of Partial Pressures"` states UNEQUIVOCALLY that in a gaseous mixture, the partial pressure exerted by a gaseous component is the SAME as it would exert if it ALONE occupied the container.

And thus `P_"He"=(n_"He"RT)/(V)=((15.2*g)/(4.0*g*mol^-1)xx0.0821*(L*atm)/(K*mol)xx295*K)/(5.00*L)`

`P_"He"=18.4*atm`

`P_(O_2)=(n_(O_2)RT)/(V)=((30.6*g)/(32.0*g*mol^-1)xx0.0821*(L*atm)/(K*mol)xx295*K)/(5.00*L)`

`P_"dioxygen"=4.63*atm`.

`"Dalton's Law of Partial Pressures"` further states that the total pressure, `P_"Total"` is the sum of the individual partial pressures.

So here `P_"Total"=P_"He"+P_(O_2)=(18.4+4.63)*atm=23.0*atm`, as required. Have another look at your calcuations. It is all too easy to make an error, and everybody has done this.