What is the PO2 of calibration gas containing 20.0% O2 when the barometric pressure is 30 in.?

To find the partial pressure of oxygen (PO2) in a calibration gas containing 20.0% O2, we first need to convert the barometric pressure from inches of mercury (in Hg) to millimeters of mercury (mm Hg).

Since 1 in Hg is equivalent to 25.4 mm Hg, a barometric pressure of 30 in Hg can be converted as follows:

30 in Hg × 25.4 mm Hg/in Hg = 762 mm Hg

Next, we use Dalton's Law of Partial Pressures, which states that the partial pressure of a gas in a mixture is equal to the total pressure multiplied by the mole fraction of the gas. In this case, the mole fraction of oxygen is 20.0%, or 0.20.

Now, we can calculate the PO2:

PO2 = Total Pressure × Mole Fraction of O2

PO2 = 762 mm Hg × 0.20

PO2 = 152.4 mm Hg

Rounding this value gives us 152 mm Hg.

This calculation illustrates how the partial pressure of a gas component can be determined from the total atmospheric pressure when the percentage composition of the gas is known. The correct choice reflects this calculated PO