Determining The Concentration Of Unknown Feii Salt

This experiment required a few equations in order to determine the concentration of [FeII] and [FeIII] as well as determine the identity of the unknown FeII salt.

y = mx + b (1)

Equation 1 was used in the context of the Beer’s Law style calibration curve seen in Figure 1.2. y represents the absorbance of the FeII solution which is directly proportional to the concentration, represented by x, of FeII in that solution. This information was essential to identify the unknown salt and calculate the concentration of FeIII.

M1V1=M2V2 (2)

Equation 2 was used to account for all the dilutions that were performed during this experiment in order to be within range of the calibration curve produced in Figure 1.2. M1 is

Obtaining the molar mass was required to identify this unknown salt to be: Fe(NH4)4(SO4)2*6H2O. Getting this result required a combination of the equations described above.

First, the absorbance of the diluted FeII solution was recorded and plugged the value into the best fit line equation from the calibration curve, giving the diluted concentration of [FeII]. In the experiment, the FeII solution was diluted by a factor of 1/100th of its original concentration, then diluted again by a factor ½ of that concentration in order to not overpower the spectrometer. Therefore, the dilution equation was then used twice to achieve the concentration of the undiluted FeII solution. This concentration was then multiplied by the total volume of solution to get the mmoles of the FeII salt. After converting mmoles to moles, the mass of this salt, weighed out at the start of the experiment, was divided by this number of moles, resulting in the molar mass in

This solution was diluted further by transferring 1.0 mL of it into a 100-mL volumetric flask, adding 40 mg of ferrozine and 1.25 mL of ammonium acetate buffer, then diluting it to volume with DI water again. Like previous solutions, this solution turned a deep purple. The absorbance spectrum of this solution was then obtained and recorded. In order to obtain an accurate spectrum, an additional serial dilution was performed to cut the concentration by a factor of