Question

What is the concentration of iron (II) in a sample of water collected from a local stream, given that the absorbance of the sample is 0.35 at a wavelength of 565 nm? The iron (II) ions form a complex with 1,10-phenanthroline, which has a molar extinction coefficient of 7.58 x 10^3 L mol^-1 cm^-1 at the same wavelength.

Answer 1

To find the concentration of iron  II  in the sample, 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 solution, and l is the path length of the light through the sample  usually in cm .In this case, we are given the absorbance  A = 0.35  and the molar extinction coefficient   = 7.58 x 10^3 L mol^-1 cm^-1  at a wavelength of 565 nm. We will assume the path length  l  is the standard 1 cm.Now, we can rearrange the equation to solve for the concentration  c :c = A /   * l Plugging in the given values:c = 0.35 /  7.58 x 10^3 L mol^-1 cm^-1 * 1 cm c = 0.35 /  7.58 x 10^3 L mol^-1 c  4.62 x 10^-5 mol L^-1So, the concentration of iron  II  in the sample is approximately 4.62 x 10^-5 mol L^-1.