# An experiment to determine the equilibrium of a complex ion using a spectrophotometer

Once the concentrations have been determined, the value for K can be calculated with an Initial-Change-Equilibrium, or ICE, table which will be explained further in the results. You've just watched JoVE's introduction to spectrophotometric determination of the equilibrium constant. Now that the data for the standard solutions has been acquired, prepare four medium test tubes containing the indicated volumes of solutions as shown in the text protocol.

## Determination of equilibrium constants

Allow the tubes to rest for 10 min. Plot the measured absorbance versus concentration of iron thiocyanate for each solution. When inserting a cuvette into the spectrophotometer, ensure that it is oriented so light passes through the transparent sides, and that the liquid level is above the path of the beam. A large excess of thiocyanate was used to ensure that all of the iron reacted, which simplifies the analysis. Cover each tube with a finger and gently shake to mix. At this steady state, the ratio of product concentrations to reactant concentrations, each raised to the power of their stoichiometric coefficients, corresponds to the equilibrium constant, K. Use a Pasteur pipette to transfer a small quantity of the mid-concentration sample, solution 3, to a cuvette, and place it in the spectrophotometer. The slope of the line, which was calculated to be , is therefore the attenuation coefficient. The equilibrium constant is calculated from the concentrations in the equilibrium row. The values are roughly constant over the range of concentrations studied. Thanks for watching! Then, the resulting RNA structure was plotted.

The concept of the equilibrium constant is important to a wide range of scientific fields. The slope of this line is the molar attenuation coefficient. Use a Pasteur pipette to transfer a small quantity of the mid-concentration sample, solution 3, to a cuvette, and place it in the spectrophotometer.

Finally, the dissociation constant — a specific type of equilibrium constant — can be used to describe protein behavior.

### Determination of an equilibrium constant lab report conclusion

Calculations Because of the complexity of the calculations in this experiment, we won't be able to provide you with a totally complete sample lab report. Use a Pasteur pipette to transfer a small quantity of solution 6 to the cuvette, and place it in the spectrophotometer. A large excess of thiocyanate was used to ensure that all of the iron reacted, which simplifies the analysis. Then, the concentrations of the remaining reactants and products can be calculated. Once the concentrations have been determined, the value for K can be calculated with an Initial-Change-Equilibrium, or ICE, table which will be explained further in the results. Because the product is formed from the reaction of iron and thiocyanate, the equilibrium concentration of each decreases by the amount of product formed. Thanks for watching! With this data, the ICE table could then be utilized. For example, the concentrations of the stock solutions, as well as the volumes of the stock solutions used for the various mixtures, are found as part of the procedure. The values are roughly constant over the range of concentrations studied.

We will illustrate, however, all the important points. Cover each tube with a finger and gently shake to mix. Realize, however, that some data is implied in the Procedure part of the experiment.

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