How many moles of molecules are in 25.5g of NO2?

Determine the molar mass of NO2 using the subscripts in the formula and the atomic weights in grams from the periodic table.

1 mole NO2 = (1 x 14.0067g N) + (2 x 15.9994g O) = 46.0055g NO2

Calculate the moles NO2 by dividing the given mass by the molar mass.

25.5g NO2 x (1mol NO2/46.0055g NO2) = 0.554mol NO2