Report Form: The Value of an Equilibrium Constant by Complex Ion Formation

(Total 80 Points)

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’ work (including your laboratory partner) or misrepresent your own data (see honor code).

Name(Print then sign): ______

Lab Partner: ______

1. Calibration Curve

Concentration / ______/ ______/ ______/ ______/ ______
Absorbance (430 nm) / ______/ ______/ ______/ ______/ ______
Absorbance () / ______/ ______/ ______/ ______/ ______

Make 2 plots of absorbance vs. concentration in order to find your value of molar absorptivity for the spectrophotometer that you used. Attach your plots to the back of this report form.

: ______

Peak Molar Absorptivity: ______

Molar Absorptivity at 430 nm: ______

Correlation Coefficient of each (): ______

2. Data

TestTube # / 1 / 2 / 3 / 4 / 5
Reagents (mL) / 1 / 2 / 3 / 4 / 5
Fe(NO3)3 / 5.00 / 5.00 / 5.00 / 5.00 / 5.00
KSCN / 1.00 / 2.00 / 3.00 / 4.00 / 5.00
0.5 M HNO3 / 4.00 / 3.00 / 2.00 / 1.00 / 0.00
Absorbance

3. Calculations

A. Calculation of assuming the reaction

  1. Find the initial number of moles of and in the mixtures in test tubes 1 through 5.
  2. Using Beer’s law, and your calibration curve, enter the experimentally determined value of [] at equilibrium for each of the mixtures in the next to last column in the table.
  3. Find the number of moles of in each of the mixtures, and enter the values in the fifth column of the table. Note that this is also the number of moles of and that were used up the reaction.
  4. From the number of moles of and initially present in each mixture, and the number of moles of and used up in forming, calculate the number of moles of and that remain in each mixture at equilibrium. Enter the results in columns 3 and 4 of the table.
  5. Find the concentrations of all of the species at equilibrium. The volume of the mixture is 10.00 mL, or 0.0100 liter in all cases. Enter the values in columns 6 and 7 of the table.
  6. Calculate for the reaction for each of the mixtures by substituting values for the equilibrium concentrations of , , and in the equilibrium expression.

Mixture / Initial # Moles / Initial # Moles / Equil # Moles / Equil # Moles / Equil # Moles / Equil. Conc. / Equil. Conc. / Equil Conc. /
Fe3+ / SCN- / Fe3+ / SCN- / FeSCN2+ / Fe3+ / SCN / FeSCN2+
1
2
3
4
5

On the basis of your results, what can you conclude about the validity of the equilibrium concept, as exemplified by Equation 2?

What do you conclude about the formula of the iron (III) thiocyanate complex ion?