Question

We were testing standard solutions of Cu(NO3)2 and a filtrate of Cu(NO3)2 using a spectrophotometer and all of the absorbances recorded were higher than what they were predicted to be.
Why might this be?

Answer 1

With no more information than that this is a guessing game. You could be using the wrong absorptivity constant, standard solution were not right, Cu(NO3)2 used to make the solution not pure, spectrometer not zeroed properly, and a host of others.