OBJECTIVE:
To determine the equilibrium constant for the following reaction:
Fe3+(aq) + SCN-(aq) -----> Fe(SCN)2+(aq)
BACKGROUND:
In this experiment, the equilibrium constant, K, for the above reaction is given by the expression:
K = [FeSCN 2+]
[Fe 3+][SCN 1-]
where the concentrations of the substances are those at equilibrium. The equilibrium concentrations of these substances will be determined and used to determine K.
Since the reactants are essentially colorless, whereas the complex ion product is deeply colored, a spectrophotometer will be used to determine the maximum absorbance due to the FeSCN2+at its four different concentrations. Beer's Law states that the absorbance of a colored solution is directly proportional to the concentration of the absorbing species. In this experiment, the FeSCN2+ is the absorbing species. The formula for Beer's Law is A = kc where A is the absorbance of the solution, k is the Beer's Law constant and c represents the concentration of the absorbing species. To make easier to calculate the equilibrium concentration of FeSCN2+, the concentration vs. absorbance is plotted on the graph. Then the formula of Beer's Law is C = kA. To make the constant k more significant number, the concentration values will be used in mmol/L.
The experiment will be done in two parts. In the first part the value of the Beer's Law constant, k, will be determined and in the second part, the Beer's Law constant and the absorbance will be used to determine the equilibrium concentration of FeSCN2+. After the equilibrium concentration of Fe(SCN)2+ will be measured by way of the absorbance, the concen...
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...sed, the equilibrium absorbance increased. The value of K is much larger than 1, so the equilibrium is said to lie to the right. The reaction is exothermic, heat is a product; the concentrations of the products are much greater than the concentrations of the reactants. The equilibrium constant is determined to be 188. This value was the same in the mixture 2 and 3. In the first mixture the K is much larger - 200, while the mixture 4 and 5 are 185 and 182. Because a balance, equilibrium constant exists when the ratio of product concentrations to reactant concentrations does not change through further reaction, there is an error in the experiment. The K values are not precise. Only two of them have the same number. The error could be done by a temperature change that is the only form of stress to an equilibrium system that changes the value of the equilibrium constant.
The mean for the temperatures is 0.116 and the solvents is 20. We predicted the 37 Celsius would be the most absorbed, but it was the -20 Celsius which can be seen in the graph above.
Use blue LED color for maximum absorbance of Ferroin and scroll down the colorimeter screen to view absorbance at your chosen wavelength. Measure the initial absorbance of the mixture with colorimeter, record it and use this information to determine the molar extinction coefficient for Ferroin. Place the cuvette into 40°C water bath and let it heat up. Remove cuvette from water bath to measure the absorbance of mixture with two minutes of interval in between, putting the cuvette immediately back after the measurement. Be sure to dry the cuvette (ex. with paper towel) before putting into colorimeter. Continue until the absorbance drops below 0.2 or when you have the 10th measurement. For second experiment, repeat procedure using 0.20M sulfuric acid by diluting 0.40M sulfuric acid. For the last experiment, use 0.40M sulfuric acid again but put into 45°C water bath instead of
Felder, M. Richard, Elementary Principles of Chemical Processes, 3rd ed.; Wiley: New Jersey, 2000; p 631.
The color that was chose to be shined through the sample was purple. The spectrophotometer was set at a wavelength of 400nm to represent the purple color. It was zeroed using the blank meaning the spectrophotometer read zero as absorbance amount. The blank consisted of 5mL of water and 2.5 mL AVM and it was placed in cuvette. A solution with a known concentration of 2.0x10-4 M was used in the spectrometer. For this solution, 5 mL of the solution with 2.5 mL of AMV was placed in the cuvette. The cuvette was placed inside of spectrophotometer and the amount of absorbance was recorded. This procedure that involves a solution with a known concentration was repeated for the concentrations:1.0x10-4 M,5.0x10-5 M,2.0x10-5M, and1.0x10-5M.A unknown solution absorbance was measured by putting 5 mL of unknown solution with 2.5 mL AMV in a cuvette. The cuvette was placed in the spectrophotometer and the amount of absorbance was recorded. The procedure that deals with the unknown solution was repeated 2 more times with the same solution and the same amount of solution and AMV. The average of the three unknown solution was calculated and the concentration of the unknown solution was
If the volume is changed, then it will have an equal effect on the concentration of reactants and of products. This is because there are an equal number of moles of gaseous substances on both sides of the arrow. Therefore, the position of the equilibrium was unaffected.
this solution we had to weigh out 5g of KHP, which is the amount needed to
This shows that there could be three variables in this experiment, carbon dioxide, water and light energy. So in our case the variable light energy (light intensity) will be used. The equation also shows that if there is more light energy then more glucose and oxygen will be produced.
2. Put the test tube inside a beaker for support. Place the beaker on a balance pan. Set the readings on the balance to zero. Then measure 14.0g of KNO3 into the test tube.
The molar absorption coefficient can be found in an absorption spectrum. The absorption spectra is generate...
A cuvette was filled 3/ 4ths of the way and the absorbance measured in a spectrophotometer. The data was compiled as a class and recorded. The Spectrophotometer was blanked using a test tube of distilled water.
The purpose of the experiment is to study the rate of reaction through varying of concentrations of a catalyst or temperatures with a constant pH, and through the data obtained the rate law, constants, and activation energies can be experimentally determined. The rate law determines how the speed of a reaction occurs thus allowing the study of the overall mechanism formation in reactions. In the general form of the rate law it is A + B C or r=k[A]x[B]y. The rate of reaction can be affected by the concentration such as A and B in the previous equation, order of reactions, and the rate constant with each species in an overall chemical reaction. As a result, the rate law must be determined experimentally. In general, in a multi-step reac...
Varying the n value carries out the experiment. Absorbencies of each of the ZLn complexes are obtained. The sum of the concentrations of the metal, Z, and the ligand, L, are kept equal. With the ratio of the ligand to the metal in the solution with the maximum absorbance for the ZLn complex, the value of n can be determined as well as the composition of ZLn.
Our most basic knowledge of chemical equilibria comes from a French man named Henry-Louis Le Chatelier. Through his studies of equlibria and the effects of changes provoked on these equilibria, he was able to come up with a principle that is studied widely today. Le Chatelier’s Principle, which was named after him, states that a change in one of the variables in a system at equilibrium will cause a shift in the position of the equilibrium that counteracts this system. Le Chatelier’s Principle is aimed at three changes that can cause a disruption in a system at equilibrium. These three changes include a change in the temperature of a reaction, a change in the concentration of one of the variable of a reaction, and a change in the pressure on a system. [1]
g. of KI in 10 mL of water. Add the KI solution dropwise to the test
Usually, potassium ion is not included due to low concentration and stable amount. Therefore, the calculation is adjusted as following: