Question

If you place one Excedrin tablet in a 250 milliliter volumetric flask what will be the concentration of each active ingredient? How would you prepare a solution that contained the active ingredients in the 20-50 microgram/mL range from the solution containing the tablet in 250 mL?

Notes: Excedrin active ingredients and dosage are Acetaminophen 250 mg, Aspirin 250 mg, and Caffeine 65 mg.

Answer 1

Given, composition of each Excedrin tablet

            Acetaminophen- 250 mg

            Aspirin             - 250 mg        

            Caffeine          - 65 mg

1 tablet is dissolved in 250 mL water (the volume of standard volumetric flask = 250 mL)

Part 1:

Concentration of Acetaminophen = mass of solute / volume of solution

= 250 mg / 250 mL

= 1 mg / Ml

Concentration of Aspirin = mass of solute / volume of solution

= 250 mg / 250 mL

= 1 mg / mL

Concentration of Caffeine = mass of solute / volume of solution

= 65 mg / 250 mL

= 0.26 mg / mL

Part 2: 1 mg = 100 microgram

We have (from part 1),

            [Acetaminophen] = 1 mg/ mL = 1000 ug/mL

            [Aspirin]          = 1 mg/ mL     = 1000 ug/mL           

            [Caffeine]        = 0.26 mg/ mL = 260 ug/mL

Using, M1V1 = M2V2 , where

C1= concentration of initial solution 1, V1= volume of initial solution 1      ;(prepare in Part 1)

C2= concentration of final solution 2, V2= volume of final solution 2            ; ;(to be prepare in Part 2)

I. For Acetaminophen

            ( 1000 ug/ mL) x V1 = (20 ug /mL) x 250 mL

            Or, V1 = 5 mL

Transfer 5 mL of initial solution to another 250-mL standard volumetric flask. Make the final solution upto the mark with distilled water.

This solution has [Acetaminophen] = 20 ug/mL

II. For Aspirin: same as above

Transfer 5 mL of initial solution to another 250-mL standard volumetric flask. Make the final solution upto the mark with distilled water.

III. for caffeine

            (260 ug/ mL) x V1 = (20 ug /mL) x 250 mL

            Or, V1 = 19.23 mL

Transfer 19.23 mL of initial solution to another 250-mL standard volumetric flask. Make the final solution upto the mark with distilled water.

This solution has [Caffeine] = 20 ug/mL

Note: A single volume of solution prepared in part 1 is NOT suitable to make a solution in range of 20-50 ug/mL of all the three ingredients.