Introduction The presence of an acid or base in the reaction medium catalyzes the reaction between acetone and iodine. CH 3 COCH 3 (l) + I 2 (aq) →CH 3 COCH 2 I (aq) + HI (aq) The immediate change in the concentration of a reactant the moment a reaction begins is the initial rate of that reaction. It is possible to establish a pattern regarding alterations in the concentrations of the reactants. Aim This experiment aimed at establishing the concentration of iodine with time by quantifying the absorbance of the reacting solution at a wavelength of 410 nanometers and finally determining the initial velocity of the reaction. It also aimed at finding the overall rate law for the reaction between iodine and acetone by comparing the rate laws of different reaction mixtures. Method The wavelength of the spectrophotometer was checked and set at 450 nanometers. The knob was adjusted until the percentage transmittance (%T) read zero with nothing in the sample holder. The spectrophotometer was then calibrated using a cuvette containing deionized water. Seven different solutions were made, each with varying amounts of 4.0 M acetone, 1.0 M HCl, and deionized water. The appropriate amount of iodine solution was finally added into the cuvette. The reactants were mixed and immediately placed in the spectrophotometer to obtain the absorbance readings at intervals of about 6 seconds. These readings were recorded in a table. A graph of absorbance against the concentration of iodine was plotted for each run. The initial rate was determined by drawing a straight line through the first two points and calculating the slope of the line. The method of initial rates was used to find the order of each reagent in the rate law of the reaction. Results The colour of the reacting mixture changed to colourless from the initial yellow-brown colour as the reaction progressed. This was because iodine concentration decreased as the reaction progressed and was reflected by a decrease in absorbance during the progress of the reaction. Table 1: Initial Reaction Rates and Reagent Concentrations of Various Runs             4.0 M    1.0 M HCl  Deionised  0.0050 M I2                        Run number  Acetone  /mL        water      /mL          Initial reaction rate             /mL                 /mL                                           1           1.5      1.5        4.0        2.0          1.834                 2           3.0      1.5        2.5        2.0          3.0776                3           4.5      1.5        1.0        2.0          3.1161                4           1.5      3.0        2.5        2.0          2.0628                5           1.5      4.5        1.0        2.0          2.2591                6           1.5      1.5        2.0        4.0          0.1065                7           1.5      1.5        0          6.0          0.1824                 The rate law for the reaction = k [CH 3 COCH 3 ] a [I 2 ] b [H + ] c . The order of the reaction was established for each reactant in the reaction using the method of isolation ( Determining reaction order n.d.). This was accomplished by comparing two investigational runs that had a discrepancy in the concentration of only one of the reactants. In the first and second runs, the concentration of acetone was changed doubling up the initial reaction rate. Therefore, the reaction was assumed a first order relating to acetone mean