A sample of oxygen gas occupies a volume of 400 mL at 50oC and 250 mmHg of pressure. What will its volume be at STP?

To solve this problem, we can use the combined gas law which states that the ratio of the product of pressure and volume and the absolute temperature of a gas is constant. The formula is:

P1V1/T1 = P2V2/T2

Where: P1 = initial pressure V1 = initial volume T1 = initial temperature P2 = final pressure V2 = final volume T2 = final temperature

Given in the problem: P1 = 250 mmHg V1 = 400 mL T1 = 50°C = 50 + 273.15 = 323.15 K (Kelvin)

Standard Temperature and Pressure (STP) is defined as 0°C and 1 atmosphere. So: P2 = 1 atm = 760 mmHg T2 = 0°C = 0 + 273.15 = 273.15 K

We are solving for V2, so rearrange the formula to solve for V2:

V2 = P1V1T2 / P2T1

Substitute the known values into the equation:

V2 = (250 mmHg * 400 mL * 273.15 K) / (760 mmHg * 323.15 K)

Calculate the above expression to find V2. This will give you the volume of the oxygen gas at STP.