Final answer:
The partial pressure of oxygen in the mixture with a total pressure of 485 mmHg and 38.8% nitrogen by mass is 297.22 mmHg.
Step-by-step explanation:
The student's question revolves around calculating the partial pressure of oxygen in a gaseous mixture of nitrogen and oxygen with a known percentage composition by mass and a given total pressure. To solve this, Dalton's Law of Partial Pressures will be used, which states that the total pressure of a mixture of gases is the sum of the partial pressures of individual gases in the mixture.
Since we know that nitrogen comprises 38.8% by mass of the mixture, we can infer that oxygen makes up the remainder, which is (100% - 38.8%) = 61.2% by mass. Given the total pressure of the mixture (485 mmHg), we can calculate the partial pressure of oxygen by multiplying this percentage by the total pressure:
Partial pressure of O2 = (61.2% / 100%) × 485 mmHg = 297.22 mmHg.