Question

A gaseous mixture of O2 and N2 contains 35.8 % nitrogen by mass. What is the partial pressure of oxygen in the mixture if the total pressure is 565 mmHg ?

Answer 1

First, change all mass to mol

assume a basis of 100 g of O2 and N2

mass of O2 = (100-35.8) = 64.2 g of O2

mass of N2= 35.8/100 = 35.8 g of N2

change to moles

mol of O2 = mass of O2 / MW of O2 = 64.2 / 32 = 2.00625

mol of N2= mass of N2/ MW of N2= 35.8 / 28 = 1.2785

Total mol = 1.2785 + 2.00625 = 3.28475

x-O2 = mol of O 2/ Total mol =2.00625 / 3.28475 = 0.611

x-N2 = mol of N2/ Total mol =1.2785/ 3.28475 =0.389

now..

P-O2 --> x-O2 * Ptotal = 0.611 * 565 mm Hg = 345.215 mm Hg of O2