1. The problem statement, all variables and given/known data I'm given the mass of an unknown sample, and the absorbance of said unknown sample. Using that and the beers law graph slope of 0.22L/mg of IronII and a y intercept I need to find the percent of the Iron II ion in the sample. 2. Relevant equations I've never heard of beers law before...I think this is the equation, but I have no clue how to use it, or which one from here to use. http://en.wikipedia.org/wiki/Beer–Lambert_law How does this law work, and how can I go about doing this calculation?