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Experiment 34 Prelaboratory Assignment An Equilibrium Constant Date Lab Sec. Name Desk No. 1. Three parameters affect the absorbance of a sample. Which one is the focus of this experiment? 2. Experimental Procedure, Part A.1, Table 34.1. A 3.00-mL aliquot of 0.001 M NaSCN is diluted to 25.0 mL with 0.2 M Fe(NO3)3 and 0.1 M HNO3. a. How many moles of SCN- are present? b. If all of the SCN- is complexed with Fe3+ to form FeNCS2+, what is the molar concentration of FeNCS2+? 3. Experimental Procedure, Part A.1. For preparing a set of standard solutions of FeNCS2+, the equilibrium molar concentration of FeNCS2+ is assumed to equal the initial molar concentration of the SCN- in the reaction mixture. Why is this assumption valid? 4. Experimental Procedure, Part A.3. The blank solution used to calibrate the spectrophotometer is 10.0 mL of 0.2 M Fe(NO3)3 diluted to 25.0 mL with 0.1 M HNO3. Why is this solution preferred to simply using de-ionized water for the calibration? 5. Plot the following data as absorbance versus [Mn+] as a calibration curve: Absorbance, A Molar Concentration of Mn+ 0.045 3.0 x 10^-4 mol/L 0.097 6.2 x 10^-4 mol/L 0.14 9.0 x 10^-4 mol/L 0.35 2.2 x 10^-3 mol/L 0.51 3.2 x 10^-3 mol/L A test solution showed a percent transmittance (%T) reading of 38.4%T. Interpret the calibration curve to determine the molar concentration of Mn+ in the test solution.

          Experiment 34 Prelaboratory Assignment
An Equilibrium Constant
Date Lab Sec. Name Desk No.
1. Three parameters affect the absorbance of a sample. Which one is the focus of this experiment?
2. Experimental Procedure, Part A.1, Table 34.1. A 3.00-mL aliquot of 0.001 M NaSCN is diluted to 25.0 mL with 0.2 M Fe(NO3)3 and 0.1 M HNO3.
a. How many moles of SCN- are present?
b. If all of the SCN- is complexed with Fe3+ to form FeNCS2+, what is the molar concentration of FeNCS2+?
3. Experimental Procedure, Part A.1. For preparing a set of standard solutions of FeNCS2+, the equilibrium molar concentration of FeNCS2+ is assumed to equal the initial molar concentration of the SCN- in the reaction mixture. Why is this assumption valid?
4. Experimental Procedure, Part A.3. The blank solution used to calibrate the spectrophotometer is 10.0 mL of 0.2 M Fe(NO3)3 diluted to 25.0 mL with 0.1 M HNO3. Why is this solution preferred to simply using de-ionized water for the calibration?
5. Plot the following data as absorbance versus [Mn+] as a calibration curve:
Absorbance, A Molar Concentration of Mn+
0.045 3.0 x 10^-4 mol/L
0.097 6.2 x 10^-4 mol/L
0.14 9.0 x 10^-4 mol/L
0.35 2.2 x 10^-3 mol/L
0.51 3.2 x 10^-3 mol/L
A test solution showed a percent transmittance (%T) reading of 38.4%T. Interpret the calibration curve to determine the molar concentration of Mn+ in the test solution.

Experiment 34 Prelaboratory Assignment
An Equilibrium Constant
Date Lab Sec. Name Desk No.
1. Three parameters affect the absorbance of a sample. Which one is the focus of this experiment?
2. Experimental Procedure, Part A.1, Table 34.1. A 3.00-mL aliquot of 0.001 M NaSCN is diluted to 25.0 mL with 0.2 M Fe(NO3)3 and 0.1 M HNO3.
a. How many moles of SCN- are present?
b. If all of the SCN- is complexed with Fe3+ to form FeNCS2+, what is the molar concentration of FeNCS2+?
3. Experimental Procedure, Part A.1. For preparing a set of standard solutions of FeNCS2+, the equilibrium molar concentration of FeNCS2+ is assumed to equal the initial molar concentration of the SCN- in the reaction mixture. Why is this assumption valid?
4. Experimental Procedure, Part A.3. The blank solution used to calibrate the spectrophotometer is 10.0 mL of 0.2 M Fe(NO3)3 diluted to 25.0 mL with 0.1 M HNO3. Why is this solution preferred to simply using de-ionized water for the calibration?
5. Plot the following data as absorbance versus [Mn+] as a calibration curve:
Absorbance, A Molar Concentration of Mn+
0.045 3.0 x 10^-4 mol/L
0.097 6.2 x 10^-4 mol/L
0.14 9.0 x 10^-4 mol/L
0.35 2.2 x 10^-3 mol/L
0.51 3.2 x 10^-3 mol/L
A test solution showed a percent transmittance (%T) reading of 38.4%T. Interpret the calibration curve to determine the molar concentration of Mn+ in the test solution.

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