Question

What is the concentration of iron (Fe) ions in a water sample collected from a river using spectrophotometry with an absorbance reading of 0.75 and known molar absorptivity of 3.6 x 10^3 L mol^-1 cm^-1? The sample has a path length of 1 cm and a volume of 25 mL.

Answer 1

To calculate the concentration of iron  Fe  ions in the water sample, we can use the Beer-Lambert Law, which states:A =  * c * lWhere:A = absorbance  0.75  = molar absorptivity  3.6 x 10^3 L mol^-1 cm^-1 c = concentration  mol L^-1 l = path length  1 cm We need to solve for the concentration  c . Rearranging the equation:c = A /   * l Now, we can plug in the values:c = 0.75 /  3.6 x 10^3 L mol^-1 cm^-1 * 1 cm c = 0.75 /  3.6 x 10^3 L mol^-1 c = 2.08 x 10^-4 mol L^-1So, the concentration of iron  Fe  ions in the water sample is 2.08 x 10^-4 mol L^-1.