Question

A Beer’s Law calibration curve was for created for an Aspirin (ASA) sample yielding the following data. Next a 100.00 mL sample of ASA was prepared. A 2.00 mL aliquot was taken from this sample and diluted to 50.00 mLs. The absorbance for this sample was 0.129. Determine the strength of the aspirin tablet. MM(ASA) = 180.16 g/mole

Answer 1

1) The absorbance of the final sample was 0.129

You have an absorbance versus concentration plot which has a straight line fit as

y= 666.68x + 0.0073

The absorbance is in th y axis and you have a y axis data. Substitue in this equation and solve for x

0.129 = 666.68x + 0.0073

0.129 - 0.0073 = 666.68x

x = 1.83 x 10^-4M

this is the concentration in the 50mL sample from which the absorbance weas measured. SO the aspirin content in this is

1.83 x 10^-4 moles/L x 0.050 L= 9.127 x 10^-6 moles

this is the amount of aspirin in the 2 mL that was added to make this solution.

9.127 x 10^-6 moles is present in 2mL

100 mL of the solution has how many moles (9.127 x 10^-6 moles x 100)/2 = 4.56 x 10^-4 moles

MW of aspirin is 180.16g/mol so 4.56 x 10^-4 moles is 4.56 x 10^-4 moles x 180.16g/mol = 0.0822 g

or 82.2 mg