Logarithmic Decay of Hypochlorite/Chlorine by UV light

chemisttree

Yes, this is what the OP expected but it is usually written as d[A]/dt = -k[A]. OP found that when concentration is plotted vs -k*ln(t) + C there is a better fit than when remaining concentration is plotted vs C₁e^-kt+ C₂.

I'm not going to analyze and replot the data so I won't comment as to why OP gets these results. I thought that perhaps a change in the quantum efficiency during the experiment might affect the best-fit curve enough to skew the results.