1. The problem statement, all variables and given/known data If I measure an absorbance at 560nm of 0.80 absorbance units for a solution of the basic form of phenolphthalein, what is the concentration of phenolphthalein? 2. Relevant equations Beer's Law -- A(sub lamda)=e*b*c 3. The attempt at a solution The question is asking for concentration, so I'll need to solve for c. I think A is the absorbance units, but beyond that I believe I'm missing information. b is supposed to be the path length, which I believe is the width of whatever cuvet is being used (the problem doesn't specify what that is). e is molar absorbtivity, but isn't that a constant? Is this problem able to be solved as it is or do I need more information? Thanks!