Are the mass percentages of 25.94% nitrogen (N) and 74.06% oxygen (O) consistent with the formula N2O5? (MN = 14.01 g mol-1; MO = 16.00 g mol-1). Explain your reasoning fully.

Answer 1

The formula N₂O₅ already has a relationship between the number of nitrogens and oxygens per molecule: 2N to 5O. Maybe we could say that out of the 7 atoms total, 2 are nitrogen (2/7)(100%) and 5 are oxygen (5/7)(100%) to get their relative percentages: 28.57% N and 71.43% O.

Not quite! Unfortunately, this ratio doesn't reflect that N and O have different molar masses! Each mole of nitrogen contributes 14.01 g each mole of oxygen contributes 16.00 g.

Total molar mass of the molecule: 2(14.01 g) + 5(16.00 g) = 108.02 g

Mass percent N: [2(14.01 g)/108.02 g](100%) = 25.94%

Mass percent O: [5(16.00 g)/108.02 g](100%) = 100% - 25.94 % = 74.06%

The answer is yes!