How many moles of c9h8o4 are in a 0.400 g tablet of aspirin?

From the periodic table:

mass of hydrogen = 1 grams

mass of oxygen = 16 grams

mass of carbon = 12 grams

This means that:

mass of one mole of aspirin = 9 (12) + 8 (1) + 4 (16) = 180 grams

number of moles can be calculated using the following rule:

number of moles = mass / molar mass

number of moles = 0.4 / 180 = 2.223 x 10^-3 moles