Consider the following reaction: Fe3+(aq)+SCN-(aq)<-->FeSCN2+(aq) A solution is

Question

Consider the following reaction: Fe3+(aq)+SCN-(aq)<-->FeSCN2+(aq) A solution is made containing an initial [Fe3+] of 1.010^?3 and an initial [SCN-] of 8.210^?4 M. At equilibrium, [FeSCN2+] = 1.610^?4 M.

Calculate the value of the equilibrium constant (Kc)

Express your answer using two significant figures.

Explanation / Answer

I used a reaction table to solve this one. .................. Fe3+(aq).... +..... SCN-(aq)... -->..... FeSCN2+(aq) Initial........ 1*10^-3M ........ 8.2*10^-4M ................. 0 Reacting....... -x ......................... -x ........................... +x Equilibrium 1*10^-3 -x ..... 8.2*10^-4 -x .............. 1.6*10^-4M They give you x so its all good. x = 1.6*10^-4 [Fe3+] = 1*10^-3 - x [Fe3+] = 1*10^-3 - 1.6*10^-4 [Fe3+] = 8.4*10^-4M [SCN-] = 8.2*10^-4 - x [SCN-] = 8.2*10^-4 - 1.6*10^-4 [SCN-] = 6.6*10^-4M Now use the equation to write the equilibrium expression and plug in the values. Kc = [FeSCN2+]/([Fe3+][SCN-]) Kc = (1.6*10^-4) / ((8.4*10^-4)(6.6*10^-4)) Kc = 288.6

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