In order to prepare a sample for absorbance readings, a vitamin tablet containing 25 mg of iron was dissolved in 6M HCl, quantitatively transferred into a 100 mL volumetric flask and diluted to the 100 mL mark with DI water. Then 20 mL and 17 mL of this solution were pipetted into separate 100 mL volumetric flasks and each of these was brought up to 100 mL volume by diluting with DI water to the mark. Required:
Calculate concentration of iron in mg/L in each of these flasks

C₂ = 50 mg/L

C₃ = 42.5 mg/L

Explanation:

To do this, we just need to use the following expression:

C₁V₁ = C₂V₂     (1)

Where:

C₁: Original concentration of the Iron solution (mg/L)

V₁: aliquot of the iron solution (mL or L)

C₂: Concentration of the iron after beind dilluted (mg/L)

V₂: Volume of the flask that's being used.

Using the above expression, we just solve for C₂:

C₂ = C₁V₁ / V₂   (2)

We have the required volumes, but we do not have the concentration of the iron solution (C₁). To determine this, we use the initial flask of 100 mL and the mass of the iron:

C₁ = 25 mg / 0.1 L = 250 mg/L

With this value, we can replace in (2) to get the concentration on each flask.

Flask 1:

We have an aliquot of 20 mL, and it was dilluted to 100 mL, the concentration would be:

C₂ = 250 mg/L * (20/100)

Flask 2:

We have an aliquot of 17 mL dilluted to 100 mL so:

C₃ = 250 * (17/100)

Hope this helps