The molar mass of aspirin is simply:
molar mass = 9 * 12 g/mol + 8 * 1 g/mol + 4 * 16 g/mol
molar mass = 180 g/mol
The number of moles is simply the ratio of mass and molar mass. therefore:
moles = 0.325 g / (180 g/mol)
moles = 1.81 x 10^-3 mol = 0.00181 mol
This problem requires mole conversion from mass to mole. To solve this, the following steps must be carried out:
STEP 1. It is easier to convert the mass of aspirin to grams at the beginning of the solution since the molar mass or molecular weight will be expressed in grams per mole.
Remember, 1 gram = 1000 mg:
[tex]mass \ of \ aspirin \ = 325.0 \ mg \times \frac{1 \ g}{1000 \ mg}\\\boxed {mass \ of \ aspirin = 0.3250 \ g}[/tex]
STEP 2. Determine the number of moles of aspirin equivalent to 0.3250 g. The molar mass will be equal to the molecular weight or the sum of the masses of the atoms that make up the compound.
To get the molar mass of aspirin, C₉H₈O₄:
[tex]molar \ mass \ of \ aspirin \ = 9(12.011 \ g) + 8(1.008 \ g) + 4(15.999 \ g)\\\boxed {molar \ mass \ of \ aspirin \ =180.159 \ g/mol}[/tex]
The number of moles of aspirin in the tablet can be determined as follows:
[tex]moles \ of \ aspirin \ = 0.3250 \ g \ C_9H_8O_4 \times \frac{1 \ mol \ C_9H_8O_4}{180.159 \ g}\\\\\boxed {moles \ of \ aspirin \ = 1.80396 \times 10^{-3} \ mol}[/tex]
Since the given has 4 significant figures, the final answer must also have 4 signfinicant digits. Therefore,
[tex]\boxed {\boxed {moles \ of \ aspirin \ = 1.804 \times 10^{-3} \ mol}}[/tex]
The number of moles of aspirin in the tablet is a very small value. This makes sense since 1 mole of aspirin will have a mass of 180.16 g. In a tablet there is only 325.0 mg which is much less than the molar mass.
Keywords: mole, molar mass
