AP Chemistry - Semester 2 : Equilibrium: the extent of Chemical Reactions

Sections: Introduction   |  Section 1   |  Section 2   |  Section 3   |  Section 4   |  Section 5   |   Lab

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Lab Assignment: Equilibrium Constant Pre-Lab Questions To be sure you are ready to begin the lab, read the following questions.  Then click on the answer to check your understanding. 1. At what point in a reaction does the reactant quotient become the equilibrium constant? The point where the amount of reactants going to products is the same as the amount of product going back to reactant, so the ratio of the product of the concentration of the products over the concentration of the reactants is unchanged. 2. What is one way you can determine the concentration of specie in the reaction? By constructing a standard curve from known concentrations of the species and the corresponding absorbance reading you can find the concentration of an unknown using its absorbency reading and plot the concentration. 3. Why do you need to pick a specific wavelength wave for the spectrophotometer, when using it to find unknown concentration of a species in a solution? The unknown has a color that is absorbed at a specific wavelength range and at other would be transparent and not show any absorbency so the concentration could not be determined 4. A standard curve is a graph that is constructed with concentration in the x axis and absorbance in the y axis, that is linear.  How would you construct a standard curve to find an unknown concentration of specie in solution? Make a series of solutions of known concentration of the specie in question and read their absorbance with a spectrophotometer. Then plot the known concentration on the x axis verses the corresponding absorbance on the y axis and connecting the point to fit a straight line. Then you can measure the unknown concentration and use the graph to find the corresponding concentration in the x axis using the absorbance reading in the y axis. Next page

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