Question

Part B

A gaseous mixture of O2 and N2 contains 40.8 % nitrogen by mass. What is the partial pressure of oxygen in the mixture if the total pressure is 245 mmHg ?

Express you answer numerically in millimeters of mercury.

Hints

Poxygen =

  mmHg  

Answer 1

Assume a basis of 100 g for simplicity

mass of N2 = 40.8% * 100g = 40.8 g of N2

mass of O2 = 100-40.8 = 59.2 g of O2

change to moles

mol of N2 = mass of N2 /MW of N2 = 40.8/28 = 1.4571 mol

mol of O2 = mass of O2 / MW of O2 = 59.2 /32 = 1.85 mol

now, total mol = 1.85 + 1.4571 = 3.3071

mol fraction of Oxygen = mol of O2 / total mol = 1.85 /3.3071 = 0.5594

now,

Partial Pressure of O2 = mol fraction of O2 * Ptotal

Partial Pressure of O2 = 0.5594 * 245

Partial Pressure of O2= 137.053 mm Hg