20 tablets weighing 2g was powdered. Exactly 50mg was transferred to
100mL volumetric flask and diluted with water. 10mL aliquot was
transferred to another 100mL and diluted to volume. The A value of the
solution was 0.652 and the absorptivity value was 15mg/mL/cm. What is
the mg of paracetamol per tablet from the following data? Please
provide a step by step solution.
According to the absorption formula:
A = a b c,
where A - absorbance (0.652), a - absorptivity (15 mg/mL/cm), b - length of path (1 cm), c - concentration.
c = A / (a b) = 0.652 / (15 mg/mL/cm × 1 cm) = 0.0435 mg/mL
As a result, the second 100 ml flask contained 0.0435 mg/mL × 100 mL = 4.35 mg of paracetamol. From here, the first 100 mL flask contained 4.35 mg × 10 = 43.5 mg of paracetamol. It means that 50 mg of tablet contains 43.5 mg of paracetamol.
Since 20 tablets weigh 2 g, one tablet weighs 2 g / 20 = 0.1 g = 100 mg.
Finally, as 50 mg of tablet contains 43.5 mg of paracetamol, one tablet (100 mg) contains 43.5 mg × 2 = 87 mg of paracetamol.
Answer: 87 mg