Essay on Determination of an Equilibrium Constant

With these absorbance numbers a concentration curve was constructed and the unknown solution was determined by finding the point of absorbance on the curve.

3ml of sample was taken first flask at 4 minutes and added to the appropriate tube of sodium hydroxide, from the second flask at 4.5 minute and so on, each flask was sampled at 30 second intervals. The sampling was then repeated starting at 8,12,16 minutes. The final sample from the last flask was taken at 18.5 minutes. Once the sampling was completed, measurements of absorbance were obtained for solution in each tube at 405 nm.

From the graph, R2 can be extrapolated from the y-axis and the corresponding value on the x-axis (the point of intersection on the curve) gives the concentration of the unknown solution.

The ending result of this experiment confirms that as five test tubes are lined up with the varying level of absorbance, different results in the level of absorbance will appear as well, this is visible in above table. Thus, this is due to the varying amount of water in the solution. The blank sample had a 0.30 in its level of absorbance.

Experimental Method: A filtration apparatus was set up. Solid iron(III) chloride hexahydrate was dissolved in water. In a separate container, sodium acetate trihydrate (NaC2H3O2 x 3 H2O) was also dissolved in water. Sodium acetate trihydrate was then added to iron(III) chloride. 2, 4-pentanedione (C5H8O2) was dissolved in methanol; it was then added to the iron(III) chloride/sodium acetate solution. The product of this mixture was filtered, and the precipitate

The isosbestic point of the acid (pH6) and basic forms (pH10) of para Nitrophenol (PNP) was expected at 350nm. As you can see in figure 2, the graph shows the intersection of 2 curves at ~350nm, which is matched with the literature value. Also, the pKa of PNP was expected 7.15 at room temperature. Refer to figure 3, the pKa is estimated to be 7.15-7.2, which very close to the literature value. In addition, the lab was succeeded in illustrating the use of a spectrophotometry to analyze concentrations of chemical substance. The absorbances of 2 unknowns were felt on the standard curve as the expectation (refer to table 4). The minimum absorbance of the known standards was 0.193 and the maximum is 1.830. The absorbance of the unknown

The Beers Law calibration experiment used many concentrations of crystal violet solutions. Each of these solutions were test and analyzed in order to determine the absorbance of each concentration The results were than graphed and produced a slope of 1.00E05 with an intercept of -2.21E-02.

Purpose: The purpose of this lab is to determine the equilibrium constant for FeSCN2+ by measuring the color absorbance of test solutions. These color absorbance values are used to determine unknown concentrations, because they are directly related to each other. These unknown concentrations can be used to find the equilibrium concentrations, which are used to find the equilibrium constant.

1) Since the [OH⁻] would double, half the required number of drops would be needed.

The absorbance is measured using a Plate reader and a Standard curve is generated. Also, the different types of pipetting techniques are assessed in this Assay.

Incorporation of assay controls included setting up a spectrophotomer and running the chart recorder with a full-scale deflection before the start of the assay. The set recorder had a corresponding value of 1 for the change in the absorbance. Therefore, prior testing was done to observe whether a change occurred in the readings. This helped to indicate that the results were valid, as they could have been affected by a fault during the setting up of the spectrophotometer. On the other hand this was considered as one of the controls for the experiment. Nevertheless, a new cuvette had to be used for each assay.

Table 2 shows the concentrations of S2O8-2 and I- and the time of each reaction for each run. Rate of the reaction was calculated by dividing 1M with the time it took to complete the reaction. The constant k was calculated using the rate law (4), the x and y value was determined by the graphs below. Considering most of the k’s calculated by our laboratory class, the supposed real value of k must be 10/Ms for that reaction.

To vary the concentrations of each reactant along with the sulphuric acid in order to observe and measure its effect on the overall rate of reaction in absorbance using colourimetry.

3 because this is the maximum absorbance for the iron (III) ion. The Beer's Law Plot that was graphed came out to be linear with an equation of:

In this lab, Le Chatelier’s Principle was observed by shifting different equilibriums to the left or right in order to make the colors of the rainbow. The equilibrium shift could be identified by the colors of the solution. In the tray 5 experiment, the reactant was pink and the product was a dark blue color. After stressing the equilibrium, a pink color indicated that the equilibrium was shifted to the left, and a blue color indicated that the equilibrium was shifted to the right. The stresses that were studied in this experiment were changes in the temperature of the system and changes in concentrations of reactants or products. Le Chatelier 's Principle states that when an equilibrium system is subject to a stress, the system responds by attaining a new equilibrium condition that minimizes the imposed stress. The main stresses on an equilibrium system are changes in concentration of the reactants or products, changes in temperature, and changes in pressure or volume for gaseous equilibria. The stress will either not cause a shift in equilibrium or will cause the system to shift left of right in order to establish an equilibrium. Adding or removing a pure solid or liquid does not change the concentration; therefore, it does not affect equilibrium. Only aqueous solutions and gases affect equilibrium. Increasing the concentration of the reactants will cause a shift to the right. Decreasing the concentration of the products also has the same effect. Decreasing the