To calculate the equilibrium concentration, you can use the ICE table approach.

Question

To calculate the equilibrium concentration, you can use the ICE table approach. ICE stands for "initial" (I), "change" (C) and "equilibrium" (E). The use of ICE tables may have been covered in your lecture. If not, please review the background knowledge posted on iCollege. Answer the following questions. In an experiment of determining the equilibrium constant of ferric thiocyanate, a student group got the absorbance vs [FeSCN^>] as shown below. In a test equilibrium system, the student group got an absorbance, 0.32. Initially, they used [Fe^3+] = 0.0010M, [SCN] = 0.00060M. Calculate the equilibrium constant of the test system. You can use the following steps to solve the problem. a. Use the absorbance vs [FeSCN^] linear equation to determine the concentration of [FeSCN^], when its absorbance is 0.32. b. Use the ICE table to determine the equilibrium concentration of [Fe^3+] and [SCN]. l (initial) C (change) E (equilibrium) c. Use the equilibrium concentration of each species to calculate the equilibrium constant. K_ = [FeSCN^2+]/[Fe^3+][SCN^]

Explanation / Answer

(a) From the graph, we get the linear fit equation:

    Y = 4312 x + 0.0075

   Absorbance = 4312 *Conc. + 0.0075

Concentration of [FeSCN-], when absorbance is 0.32

   0.32 = 4312 *Conc. + 0.0075

(0.32 – 0.0075)/ 4312 = Conc.

Concentration of [FeSCN-] = 7.23 x 10-5 M

(b) ICE table not given in the question.

(c) because we can not calculate the equlibrium concentrations and Kc value without ICE table.

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