The pressure in a vessel that contained pure oxygen dropped from 2000 torr to 1500 torr in 50 minutes as the oxygen leaked through a small hole into a vacuum. When the same vessel was filled with another gas, the pressure dropped from 2000Torr to 1600Torr in 80 minutes. What is the molar mass of unknown gas?

Explanation

To solve the problem step by step, we will use Graham's law of diffusion, which relates the rates of diffusion of two gases to their molar masses.

### Step 1: Determine the change in pressure for both gases.
- For oxygen (O2):
- Initial pressure = 2000 torr
- Final pressure = 1500 torr
- Change in pressure (ΔP_O2) = 2000 torr - 1500 torr = 500 torr

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