Air is about 78% nitrogen gas (N2) by mass. The molar mass of nitrogen gas is 28.0 g/mol. A 100.0-g sample of air contains how many moles of nitrogen
To solve, first convert the 78% to 78 grams (100g of air will contain 78 grams of nitrogen). Then, you will multiply 78 grams by 1 mol/28 g: 78 x (1/28) The grams will cancel out, leaving you with 2.79 moles.