18) Aspirin is a monoprotic acid called acetylsalicylic acid. Its formula is HC9H7O4. A certain pain reliever was analyzed for aspirin by dissolving 0.534 g of it in water and titrating it with 0.0446 M KOH solution. The titration required 26.73 mL of base. What is the percentage by weight of aspirin in the drug?
mols KOH = M x L = ?
Since aspirin is a monoprotic acid then mols aspirin = mols KOH.
g aspirin = mols aspirin x molar mass aspirin.
% aspirin = (mass aspirin/0.534)*100 =
To find the percentage by weight of aspirin in the drug, we need to determine the number of moles of aspirin present in the given sample.
First, we calculate the number of moles of KOH used in the titration. The molarity (M) of KOH is given as 0.0446 M, and the volume (V) used is 26.73 mL, which is equivalent to 0.02673 L:
Number of moles of KOH = Molarity × Volume
= 0.0446 mol/L × 0.02673 L
= 0.00119 mol
Since the stoichiometric ratio between KOH and acetylsalicylic acid (aspirin) is 1:1, the number of moles of acetylsalicylic acid is also equal to 0.00119 mol.
Next, we calculate the molar mass of acetylsalicylic acid using its formula, HC9H7O4:
Molar mass of acetylsalicylic acid = (1 × 1.01 g/mol) + (9 × 12.01 g/mol) + (7 × 1.01 g/mol) + (4 × 16.00 g/mol)
= 180.16 g/mol
Now, we can calculate the mass of acetylsalicylic acid in the 0.534 g sample:
Mass of acetylsalicylic acid = Number of moles × Molar mass
= 0.00119 mol × 180.16 g/mol
= 0.214 g
Finally, we can determine the percentage by weight of aspirin in the drug by dividing the mass of acetylsalicylic acid by the mass of the sample and multiplying by 100:
Percentage by weight = (Mass of aspirin / Mass of sample) × 100
= (0.214 g / 0.534 g) × 100
= 40.07%
Therefore, the percentage by weight of aspirin in the drug is approximately 40.07%.