You will prepare and submit a term paper on Finding the Equilibrium Constant. Your paper should be a minimum of 1250 words in length. This experiment will find the equilibrium constant in the reaction that forms thiocyanoiron. .
After equilibrium, if established, a colorimeter is used to determine the absorbance (and by extension the concentration) of the thiocyanoiron complex formed. This is then used to determine the concentration of the Fe3+ and SCN-. The concentrations obtained are then used in the Kc equation above to find the equilibrium constant. The colorimeter makes use of Beer’s law (Abs = εlc) to determine the concentration1. The molar absorptivity of FeSCN2+ will be obtained by making use of a standard solution containing Fe3+ ions in excess, and by employing Le Châteliers principle to describe the shift of the reaction to the right (thus promoting the formation of the product), and in the process utilizing the all of the available SCN- ions2. As a result, the [FeSCN2+] in the equilibrium is equivalent to the amount of SCN- that was initially available3. Because the mole ratio is 1:1, and also because the initial concentrations are known, the concentration of the unreacted reactant can be found by finding the difference between the initial concentration of the reactant and the equilibrium concentration of the product4.
5.00 mL of 0.00200 M Fe(NO3)3 was pipetted into four different labeled test tubes. The volumes were recorded. 25 mL of 0.00200 M KSCN was poured into a dry 100 mL beaker and then 2.00, 3.00, 4.00 and 5.00 mL pipetted into the test tubes labeled initially. The volume used was recorded. 25 mL of distilled water was placed in a 100 mL beaker and then 3.00, 2.00, 1.00 and 0.00 mL of this water pipetted into the four labeled test tubes. The actual volumes of the test tubes were recorded. Each solution was mixed thoroughly with a plastic dropper. The temperature of one of the four solutions was measured and recorded. this was to be used in measuring the equilibrium constant, Kc.
A standard solution of FeSCN2+ was prepared by pipetting 18 mL of 0.200 M Fe(NO3)3 into a 25 x 150 mm test tube labeled “5”.  .2.00 mL of 0.00200 M KSCN was pipetted into the same test tube.