Question

What is the concentration of iron(II) ions in a sample of water collected from a local pond using colorimetry, if the measured absorbance of the sample at 565 nm is 0.673 and the molar absorptivity of the iron(II) complex at this wavelength is 20,500 M⁻¹·cm⁻¹?

Answer 1

To find the concentration of iron II  ions in the sample, we can use the Beer-Lambert Law, which states:A =   c  lwhere A is the absorbance,  is the molar absorptivity, c is the concentration of the solution  in mol/L or M , and l is the path length of the cuvette  in cm .In this case, we have:A = 0.673 = 20,500 Mcml = 1 cm  assuming a standard cuvette We need to solve for c  the concentration of iron II  ions :0.673 = 20,500  c  1Now, we can isolate c:c = 0.673 / 20,500c  0.0000328 MSo, the concentration of iron II  ions in the sample is approximately 0.0000328 M or 32.8 M.