[lazy167]

Hi
I been given a experiment at college where i have to calculate the rate constant of aquation, i've been given some readings which i don't really understand but it does tell me that the mechanism is actually second order but to treat it as a pseudo first order reaction.
Ok so i did in the lab was make up a water solution of cis-[Cr(en)2Cl2]Cl.H20 where the initial concentration was 5 x 10^-3 M. I was then asked to run UV-VIs multi scan spectrum where it took readings every 2mins for 30mins.

cis-[Cr(en)2Cl2]Cl.H20 +H20 ---k--> cis-[Cr(en)2Cl(OH2)]Cl.H20 + Cl-

Once i got the data , i choose a specific wavelength eg 500nm  then i took the absorbance of all 15 scans of the solution at 500nm. and i plotted a graph of the absorbance against time and added a trendline (polynomial) to get the slope. However the value i got for the slope(rate constant) is nowhere near the theoretical value in the reading.

I'm just wondering if i went about calculating the rate constant correctly? If not how do i go abouts doing it.

Thank you and sorry if this sounded confusing