The purpose of this lab is to solve for the equilibrium constant of a reaction between iron (iii) ions and thiocyanate ions. The lab is divided into two parts: one section recording absorbance of reference solutions and the other part for the absorbance of test solutions. The reference solutions were created through the mixing of excess iron (iii) nitrate (Fe(NO3)3) with a known concentration of potassium thiocyanate (KSCN) in order to push the reaction to completion; the initial concentration of thiocyanate equates to the equilibrium concentration of monothiocyanatoferrate (iii) (FeSCN2+). The test solutions are a combination of water, KSCN, and Fe(NO3)3, where the volume of iron (iii) nitrate is kept constant; here, the concentration of
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Many concepts and theories were covered throughout this lab. To find the equilibrium constant of FeSCN2+ one needed to find the equilibrium concentration of the compound. In order to do this, Beer’s Law, which relates absorption to concentration, was implemented. The reference solutions were created as a way to formulate a Beer’s Law plot by way of measuring a known concentration of FeSCN2+ and measuring its absorption; varying amounts of each reaction were mixed together in a solution to have multiple points on the plot. When mixing the compounds together, a dilution occurs, where both reactants have a …show more content…
The first lab error noted had to do with scratches on the test tubes used for the spectrophotometer. When inserting the tube into the Spec-20, slight scratches and damage on the tube might result in some light refraction; this would cause a slight aberration of absorption values. The liquids inside the test tubes would give off a reading greater than its actual absorption because of the scratches on the test tube. Used in the Beer’s Law plot, the slightly flawed reference solutions would increase the slope of the line, affecting concentration values plugged in later. It would increase the equilibrium concentration of the FeSCN2+ and thereafter, increase the equilibrium constant for the reaction. The second lab error in the experiment had to do with the reference reactions. Rather than creating a dynamic equilibrium, like that of the reactions in the test solutions, the reference solutions were made to push the reaction to completion; in other words, all of the 0.0002 M KSCN needed to react with the 0.200 M Fe(NO3)3. With the disproportionately large concentration of Fe(NO3)3 compared to the KSCN, the Fe(NO3)3 became the excess reactant, while the KSCN becomes the limiting reactant. The Fe(NO3)3, being a colored solution of reddish brown, would still be present in the solution after the reaction occurred. This would cause an issue because the coloration of the solution would not solely be FeSCN2+, but rather a
Many concepts and theories were covered throughout this lab. To find the equilibrium constant of FeSCN2+ one needed to find the equilibrium concentration of the compound. In order to do this, Beer’s Law, which relates absorption to concentration, was implemented. The reference solutions were created as a way to formulate a Beer’s Law plot by way of measuring a known concentration of FeSCN2+ and measuring its absorption; varying amounts of each reaction were mixed together in a solution to have multiple points on the plot. When mixing the compounds together, a dilution occurs, where both reactants have a …show more content…
The first lab error noted had to do with scratches on the test tubes used for the spectrophotometer. When inserting the tube into the Spec-20, slight scratches and damage on the tube might result in some light refraction; this would cause a slight aberration of absorption values. The liquids inside the test tubes would give off a reading greater than its actual absorption because of the scratches on the test tube. Used in the Beer’s Law plot, the slightly flawed reference solutions would increase the slope of the line, affecting concentration values plugged in later. It would increase the equilibrium concentration of the FeSCN2+ and thereafter, increase the equilibrium constant for the reaction. The second lab error in the experiment had to do with the reference reactions. Rather than creating a dynamic equilibrium, like that of the reactions in the test solutions, the reference solutions were made to push the reaction to completion; in other words, all of the 0.0002 M KSCN needed to react with the 0.200 M Fe(NO3)3. With the disproportionately large concentration of Fe(NO3)3 compared to the KSCN, the Fe(NO3)3 became the excess reactant, while the KSCN becomes the limiting reactant. The Fe(NO3)3, being a colored solution of reddish brown, would still be present in the solution after the reaction occurred. This would cause an issue because the coloration of the solution would not solely be FeSCN2+, but rather a