Photosynthesis Lab

Purpose The purpose of this experiment is to determine K, the rate constant k1 of the forward reaction divided by the rate constant k-1, as well as Ymax, which is the maximum number of moles of acetic acid that can be adsorbed on the surface of the charcoal, per gram of charcoal.

Methods A finely powdered charcoal is placed in an acetic acid solution, and some of the acetic acid molecules can be removed from the solution by adsorption on the surface of the charcoal solid. Equilibrium can eventually be established between the acetic acid adsorbed on the surface of charcoal and the unbound acetic acid in the solution. The amount of acetic acid adsorbed onto the surface of the charcoal can be determined through the titration of the original

C is plotted and fitted to a logarithmic-line to illustrate the saturation effect, shown in Figure 1. Then using equation 12.8 in the lab manual, C/Y is calculated and plotted versus C and fitted to a straight line, shown in Figure 2. From the fitted line, Ymax, which is the maximum number of moles of acetic acid that can be adsorbed on the surface of the charcoal per gram of charcoal, can be calculated from the slope. Then, using Ymax and the value of the y-intercept, K, which is the ratio between the rate constant k1 of the forward reaction (adsorption on the charcoal) and the rate constant k-1 (detachment from the charcoal), can be determined. For calculations, refer to Appendix E. Finally, multiplying Ymax by Avagadro’s number will give the number of AA molecules adsorbed on the surface of one gram of charcoal at saturation. Since the approximate surface area occupied by a single AA molecule is 2.1E-19 m2, one can calculate the total surface area of one gram of charcoal. For calculations, refer to Appendix F. Note that all uncertainties from several dilution steps, weighing of the charcoal, the titration steps, and every measurement are taken into account when determining Y and C/Y. The calculated uncertainties are used to draw the error bars on the plots in Figure 1 and Figure