Question

What is the concentration of iron (II) ions in a water sample with absorbance of 0.295 at a wavelength of 510 nm, given that the molar extinction coefficient of iron (II) ions is 11,300 M^-1cm^-1 at this wavelength? Use colorimetry to determine the solution.

Answer 1

To determine the concentration of iron  II  ions in the water sample using colorimetry, we can use the Beer-Lambert Law, which states:A =  * c * lwhere A is the absorbance,  is the molar extinction coefficient, c is the concentration of the solute  in this case, iron  II  ions , and l is the path length of the cuvette  usually in cm .We are given the following values:A = 0.295 = 11,300 M^-1cm^-1l = 1 cm  assuming a standard cuvette Now, we can rearrange the equation to solve for the concentration  c :c = A /   * l Plugging in the given values:c = 0.295 /  11,300 M^-1cm^-1 * 1 cm c  0.0000261 MSo, the concentration of iron  II  ions in the water sample is approximately 0.0000261 M or 26.1 M.