Question 12.27: Using Dalton's Law to Calculate a Partial Pressure An unknow......
Using Dalton’s Law to Calculate a Partial Pressure
An unknown quantity of the noble gas xenon (Xe) is added to a cylinder already containing a mixture of the noble gases helium (He) and argon (Ar) at partial pressures, respectively, of 3.00 atm and 1.00 atm. After the Xe addition, the total pressure in the cylinder is 5.80 atm. What is the partial pressure, in atmospheres, of the Xe gas?
The partial pressures of the He and Ar in the mixture will not be affected by the addition of the Xe (Dalton’s law). Thus, the partial pressures of the He and Ar remain at 3.00 atm and 1.00 atm, respectively.
The sum of the partial pressures of He and Ar is 4.00 atm.
3.00 atm + 1.00 atm = 4.00 atm
The difference between this pressure sum and the total pressure in the cylinder is caused by the Xe present. Thus, the partial pressure of the Xe is
P_{\textrm{Xe}} = P_{\textrm{total}} – (P_{\textrm{He}} + P_{\textrm{Ar}})= 5.80 atm – 4.00 atm = 1.8 atm (calculator answer)
= 1.80 atm (correct answer)