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, we will use Graham's law of diffusion, which states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Identify the Changes in Pressure and Time:**
- For oxygen (O₂):
- Initial pressure (P1) = 2000 torr
- Final pressure (P2) = 1500 torr
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