[lunchly]

I'm investigating the effect of pH on the extent of hydrolysis of aspirin, where I react an aspirin solution with FeCl3 to make a colored complex and measure spec absorbance. I did my pilot testing today but my solutions turned out cloudy with some solid still left in it because the aspirin wasn't fully dissolved. Then, adding FeCl3 turned it colored but still cloudy. My absorbance values for a very acidic and very basic pH group were almost the exact same and I was wondering if the cloudiness was the reason why or because the wavelength doesn't work (550nm) for the ranges of color? From acidic to basic pH, the color of the solutions ranged from violet (pH 3) to orange-ish (pH 10).

[Corribus]

If your solutions are cloudy, UV-Vis measurements will not be very reliable. Suspended particles in solution will scatter light. Consider using a lower concentration or taking other steps to ensure good dissolution.

Also capturing optical density readings at a single wavelength will not be a reliable way to spectrometrically track a reaction where the color changes dramatically. This is probably a sign that your complex has more than one absorption band or you have two species in solution that absorb at different wavelengths (optical density increasing at one wavelength while it decreases at another). In a case like this you would want to monitor a range of wavelengths and look for isosbestic behavior so that you can choose an appropriate wavelength to monitor your reaction.

[Babcock_Hall]

Have you thought about Fe(OH)₃?

[marquis]

If dealing with aspirin tablets, there are sometimes fillers added. When dissolved, they show well.in turbidity, but mess up absorbance or transmittance.  Sometimes the fillers give the results you are talking about.  After crushing the aspirin and disdolving it, try running it through coffee filters. Sometimes, this can be filtered out.  The particulate is very fine so this might not work.  But its worth a try!