Question

How many molecules of aspirin (c9h8o4) are there in a 246 mg tablet of aspirin? answer in units of molec?

Answer 1

Let's compute the molar mass of aspirin first by looking at its chemical formula.

Molar mass = 9(12 g/mol) + 8(1 g/mol) + 4(16g/mol) = 180 mg/mmol

Thus,
Moles aspirin = 246 mg * 1 mmol/180 mg * 1 mol/1000 mmol = 1.367×10⁻³

Now, according to Avogadro, there are 6.022×10²³ molecules for every mole of any substance. Therefore,

Molecules of aspirin = 1.367×10⁻³ mol * 6.022×10²³ molecules/mol
Molecules of aspirin = 3.23×10²⁰