Question

Determination of Iron in Vitamin Supplements by Spectrophotometric Analysis

A tablet containing iron, Fe (II) fumarate (Fe2+C4H2O4 2- ) and binder was dissolved in 0.1M HCl solution and the solution was filtered to remove any insoluble binder

Fe (II) in the above step was oxidized with hydrogen peroxide to Fe (III) as follows 2 Fe2+ + H2O2 + H+ → 2 Fe3+ + 2 H2O

The solution prepared in above step 3 was transferred to a 1000 mL volumetric flask. To this flask, 1M potassium thiocyanate (KSCN) was added and volume was brought to 1000 mL with water. Reaction of Fe (III) with KSCN formed a blue color solution.

Fe3+(aq) + SCN- (aq) Fe(SCN)2+(aq)

UV absorbance at 477 nm was measured for the solution prepared in step 3 and the absorbance value was recorded in the laboratory notebook

Steps 1 through 4 was repeated for additional 5 tablets (six tablets total). 6. Following are the UV absorbance values for the FeSCN complex prepared for each tablet.

Following are the UV absorbance values for the FeSCN complex prepared for each tablet.

Tablet Number               Absorbances

1 0.639

2                              0.683

3                              0.702

4                              0.732

5                              0.722

6                              0.767

A calibration curve was prepared from a ferric chloride (FeCl3) standards from 20 to 60 µg/mL concentration range that provided the following absorbance values.

Fe (µg/mL)      Absorbance @450nm

10                           0.434

20                           0.566

30                           0.625

40                          0.880

50                           1.002

The mass of iron in milligram in each tablet was recorded in the laboratory notebook. Calculate the mass of iron from the two tables for each tablet using the spectrophotometric method (Remember to correct for the dilution factor).

I made the Calibration Curve and got this equation.

y = 16.92x + 0.0064

How do I solve for the mass of iron using this equation?

Answer 1

Your calibration curve equation,

y = 16,92x + 0.0064

here,

y = absorbance

x = concentration

So, in order to find the concentration in the tablet, just feed in the absorbance values in place of y and that should give the concentration x.

Tablet No.   Absorbance      Concentration (M)

    1                  0.639            (0.639 - 0.0064)/16.92 = 0.037 M

    2                  0.683            (0.683 - 0.0064)/16.92 = 0.040 M

    3                  0.702            (0.702 - 0.0064)/16.92 = 0.041 M

    4                  0.732            (0.732 - 0.0064)/16.92 = 0.043 M

    5                  0.722            (0.722- 0.0064)/16.92 = 0.042 M

    6                  0.767            (0.767 - 0.0064)/16.92 = 0.045 M