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A student mixes 5.0 mL of 0.00200 M Fe(NO3)3 with 5.0 mL 0.00200 KSCN. She finds that the concentration of FeSCN2+ in the equilibrium mixture is 0.000125 M. Follow these steps to determine the corresponding experimental value of Kc for the reaction of Fe3+ and SCN- to produce this complex ion. Show your calculations for each step below and then place the appropriate value(s) in the equilibrium (or 'ICE') table near the bottom of the page. Step 1. Calculate the molarity of Fe3+, SCN-, and FeSCN2+ initially present after mixing the two solutions, but prior to any reaction taking place. (M1V1 = M2V2) Fe3+ : SCN- : FeSCN2+ : Step 2. Determine the expression and initial value for Qc. Then give the appropriate signs of the concentration changes for each species in terms of the reaction's shift, or x, into the 'ICE' table. Step 3. Fill in the equilibrium value for the molarity of FeSCN2+. From this, you can determine the value of x. Step 4. Given the value of x, determine the equilibrium molarities of Fe3+ and SCN-. 'ICE' Table Fe3+ (aq) + SCN- (aq) ? FeSCN2+ (aq) I C E Step 5. Give the correct expression for Kc for this equation. Then calculate the value of Kc for the reaction from the equilibrium concentrations. Use correct significant figures. Step 6. On the reverse side, complete an 'ICE' table using this same procedure, but using a different reaction stoichiometry: Fe3+ + 2 SCN- ? FeSCN2+. Assume that the equilibrium concentration of FeSCN2+ is 0.0000625 M, or one-half its previous value. Remember how the reaction stoichiometry affects the expression for Kc.

A student mixes 5.0 mL of 0.00200 M Fe(NO3)3 with 5.0 mL 0.00200 KSCN. She finds that the concentration of FeSCN2+ in the equilibrium mixture is 0.000125 M. Follow these steps to determine the corresponding experimental value of Kc for the reaction of Fe3+ and SCN- to produce this complex ion. Show your calculations for each step below and then place the appropriate value(s) in the equilibrium (or 'ICE') table near the bottom of the page.

Step 1. Calculate the molarity of Fe3+, SCN-, and FeSCN2+ initially present after mixing the two solutions, but prior to any reaction taking place. (M1V1 = M2V2)
Fe3+ : SCN- : FeSCN2+ :

Step 2. Determine the expression and initial value for Qc. Then give the appropriate signs of the concentration changes for each species in terms of the reaction's shift, or x, into the 'ICE' table.

Step 3. Fill in the equilibrium value for the molarity of FeSCN2+. From this, you can determine the value of x.

Step 4. Given the value of x, determine the equilibrium molarities of Fe3+ and SCN-.

'ICE' Table
Fe3+ (aq) + SCN- (aq) ? FeSCN2+ (aq)
I
C
E

Step 5. Give the correct expression for Kc for this equation. Then calculate the value of Kc for the reaction from the equilibrium concentrations. Use correct significant figures.

Step 6. On the reverse side, complete an 'ICE' table using this same procedure, but using a different reaction stoichiometry: Fe3+ + 2 SCN- ? FeSCN2+. Assume that the equilibrium concentration of FeSCN2+ is 0.0000625 M, or one-half its previous value. Remember how the reaction stoichiometry affects the expression for Kc.

A student mixes 5.0 mL of 0.00200 M Fe(NO3)3 with 5.0 mL 0.00200 KSCN. She finds that the concentration of FeSCN2+ in the equilibrium mixture is 0.000125 M. Follow these steps to determine the corresponding experimental value of Kc for the reaction of Fe3+ and SCN- to produce this complex ion. Show your calculations for each step below and then place the appropriate value(s) in the equilibrium (or 'ICE') table near the bottom of the page.

Step 1. Calculate the molarity of Fe3+, SCN-, and FeSCN2+ initially present after mixing the two solutions, but prior to any reaction taking place. (M1V1 = M2V2)
Fe3+ : SCN- : FeSCN2+ :

Step 2. Determine the expression and initial value for Qc. Then give the appropriate signs of the concentration changes for each species in terms of the reaction's shift, or x, into the 'ICE' table.

Step 3. Fill in the equilibrium value for the molarity of FeSCN2+. From this, you can determine the value of x.

Step 4. Given the value of x, determine the equilibrium molarities of Fe3+ and SCN-.

'ICE' Table
Fe3+ (aq) + SCN- (aq) ? FeSCN2+ (aq)
I
C
E

Step 5. Give the correct expression for Kc for this equation. Then calculate the value of Kc for the reaction from the equilibrium concentrations. Use correct significant figures.

Step 6. On the reverse side, complete an 'ICE' table using this same procedure, but using a different reaction stoichiometry: Fe3+ + 2 SCN- ? FeSCN2+. Assume that the equilibrium concentration of FeSCN2+ is 0.0000625 M, or one-half its previous value. Remember how the reaction stoichiometry affects the expression for Kc.

Added by Stephanie J.

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