A mixture of gases contains 319 torr N2, 273 torr O2, and 285 torr Ar. What is the total pressure of the mixture?
The total pressure of the mixture will be
When dealing with mixtures of gases, you must keep in mind that the total pressure of the mixture can be broken down as a sum of the partial pressures of all the individual gases that make up that mixture - this is known as Dalton's law.
In other words, each gas that's part of the mixture adds its partial pressure to the total pressure exercited in the container.
Imagine that you start with an empty flask. You put the nitrogen in first and record its pressure - 319 torr. Then you get it out, put in the oxygen, and record its pressure - 273 torr.
Finally, you get the oxygen out, put in the argon, and record its pressure - 285 torr.
Now, it only makes sense that when you put all three gases together in the same flask, the total pressure will be the sum of their individual pressures. When in the mixture, these individual pressures will become their partial pressures.