Question

Prepare a solution of tabletop sweetener by weighing approximately 400 mg of sweetener powder directly into a 10.00 ml volumetric flask. Recorded the exact mass of the sugar used. Add 5 ml of standard Aspartame solution to dissolve the powder and then add 2.00 ml of reagent. Finally, dilute to volume with water. Wait 15 minutes and record the solution absorbance. Used the standard curve to determine the mass of aspartame per gram of sweetener by application of Law. Will the student be able to determine the correct amount of Aspartame present in sugar sample? If not, why?

Answer 1

Ans. Yes, the student would be able to calculate the mass of aspartame present in sugar sample.

It is the case of “Standard Addition method”.

Steps:

Part 1: Calculate increase in [Aspartame] due to standard addition (spiking)

Original solution: 400.0 mg sugar sample is dissolved in 10.0 mL volume.

Spiked solution: 5.0 mL standard aspartame is mixed with 400.0 mg tablet and diluted to 10.0 mL solution. So, the spiked solution has higher [Aspartame] than that of the original solution.

Increase in [Aspartame] of spiked solution is given by C2 in -

            C1V1 (standard aspartame) = C2V2 (increased aspartame in spiked solution)

            C1 x 5.0 mL = C2 x 10.0 mL

Since, standard [aspartame] = C1 = Known ; C2 can be calculated from above expression.

Part 2: Let, Abs of original (un-spiked) sugar solution = X

                        Abs of spiked-sugar solution = Y

            Increase in Abs due to spiking = Y – X

Since X and Y are experimentally determined, the increase in Abs can easily be calculated as (Y - X).

Now,

Since, the increase in Abs by (Y - X) units is solely due to addition of Aspartame standard, an Abs of (Y-X) units is equivalent to “C2”- the increase in [Aspartame] due to spiking.

So,

            (Y-X) units Abs is equivalent to C2 aspartame

     Or, 1 unit -           -           -          [C2 / (Y-X)]

     Or, X units-           -           -           [C2 / (Y-X)] x X

In the above expression all the variables (C2, X and Y) are known. SO, concentration of aspartame in the original sugar solution is determined as “[C2 / (Y-X)] x X”          

# Once [aspartame] in original solution is known, the mass of aspartame and relative amount per unit mass of sugar tablet can also be determined.