An aspirin tablet contains 325 mg of acetylsalicylic acid (C₉H₈O₄). How many acetylsalicylic acid molecules does it contain?

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SORT You are given the mass of acetylsali- cylic acid and asked to find the number of molecules. STRATEGIZE First convert to moles (using the molar mass of the compound) and then to number of molecules (using Avogadro's number). You need both the molar mass of acetylsalicylic acid and Avogadro's number as conversion factors. You also need the conversion factor between g and mg. GIVEN: 325 mg C,H,O4 FIND: number of C9H8O4 molecules CONCEPTUAL PLAN mg C₂H₂O4 10³ g 1 mg g C₂H8O4 mol C₂H₂O4 6.022 x 1023 1 mol 1 mg = 10-3, ³g 1 mol C₂H₂O4 180.15 g C₂H8O4 number of CoHgQ4 molecules 6.022 x 1023 C₂H8O4 molecules 1 mol C₂H₂O4 RELATIONSHIPS USED C₂H8O4 molar mass= 9(12.01) + 8(1.008) + 4(16.00) = 180.15 g/mol