# Molar Absorptivity of Copper(II) Sulfate

What is the molar absorptivity of copper sulfate? I am trying to find the molarity of copper sulfate solution by absorption in a spectrophotometer with a cuvette.

However, I can't find $$\varepsilon$$, the molar absorptivity coefficient of $$\ce{CuSO4}$$. I searched it up online, and I found experimental data saying that is $$\pu{2.81 L mol-1 cm-1}$$, but another source says that it is $$0.91$$.

I have searched on various databases including NIST's, but I couldn't find anything. Is there a definite molar absorptivity for everything, or is it all experimental?

• The value will depend on wavelength so both the values above could be correct; it would be worth checking. Also if you can, measure absorbance vs. concentration. The eqn. is $A=\epsilon [C]l$ where l is the cell path length and $\epsilon$ the extinction coefficient in $\pu{dm^2mol^{-1}cm^{-1}}$ – porphyrin May 13 '17 at 12:11
• Right, I searched up 635nm, but I forgot to make sure that it was actually that. Thanks for reminding me – abcdefg May 13 '17 at 20:08