Question

Pre-Lab Questions

1. What is the literature value for the formation constant (Kf) for FeSCN2+?

2. Write the balanced chemical equation for the formation of FeSCN2+ from FeCl3·6H2O and NaSCN.

3. In this experiment a dilute solution of 0.1 M HNO3 is used to maintain the ionic strength and low pH needed for the reaction to occur. How is nitric acid classified in terms of MSDS? What are some of the safety concerns regarding the handling of nitric acid?

4. Look at the procedure for making the standard solutions. What is the molar ratio of Fe3+ to SCN- in solution S3?

5. What is the λmax for the Absorption of FeSCN2+ in 0.1 M HNO3?

6. For the second part of the experiment, you will need a working stock solution that is approximately 0.002 M Fe3+. Describe exactly how you will prepare a 0.002 M Fe3+ solution from a stock solution that was made using 27.03 g of FeCl3·6H2O in 500 mL of 0.1M HNO3.

7. In the second part of the experiment, you will collect absorbance data for a series of mixtures of Fe3+ and SCN-. Prepare a sample data table that you will need in order to complete the ICE table and make the calculation for the equilibrium constant.

8. Given that the molar absorptivity constant for FeSCN2+ is 63.7 (mg/mL)-1cm-1, calculate the molar concentration in moles/L of FeSCN2+ in a solution with a λmax absorption of 0.62.

Procedure

Part A – Calibration Curve for Spectrophotometric Determination of FeSCN2+

Preparing Calibration Standards for FeSCN2+

1. Label six 25.00-ml volumetric flasks S1 through S6.
2. Prepare six FeSCN2+ calibration standards (S1-S6) according to Table 1 below. Begin by delivering 4.00 mL of 0.2 M Fe3+ solution into each of the volumetric flasks.
3. Using a micropipette, deliver the requisite amount of 0.002 M NaSCN solution to each flask according to Table 1. Fill flasks to the mark with 0.1 M HNO3 and mix thoroughly.

Experiment 6: Equilibrium Constant 4

Solution	Vol 0.2 M Fe3+ (mL)	Vol 0.002 M NaSCN (mL)	Final Volume (mL)
S1	4.00	0.00	25.00
S2	4.00	0.20	25.00
S3	4.00	0.40	25.00
S4	4.00	0.80	25.00
S5	4.00	1.20	25.00
S6	4.00	1.60	25.00

Table 1. Standard Solutions for FeSCN2+ ion Calibration Curve

PLEASE HELP ME ANSWER PRE-LAB QUESTIONS 1-8! THANK YOU

Answer 1

1. The literature value for the formation constant (Kf) for [FeSCN]²⁺ is 8.9 x 10².

2. The balanced chemical equation for the formation of FeSCN2+ from FeCl3·6H2O and NaSCN is:

NaSCN + FeCl₃*6H₂O = [FeSCN]Cl₂ + NaCl + 6 H₂O

3. Nitric acid is composed of 65% nitric acid (fuming) and 35% water.

It is very hazardous in case of eye contact (causes redness, watering, itching), skin contact (causes burns). It is slightly hazardous when its vapours inhaled (causes irritation in respiratory tract). Exposure to a long time to the substance can produce target organs damage, even may cause death.

Safety measures: Don't ingest. Don't breath its fumes. Keep away from ignition. Keep it locked in store. Keep the container dry. Keep it away from fire catching material. Handle it with gloves in hands. Wear labcoat. Wear glasses to protect eyes.

4. In S3, moles of Fe3+ = (0.2*4)/1000= 0.8/1000

Moles of NaSCN- = (0.002*0.4)/1000= 0.0008/1000

Fe3+: NaSCN- = 1000:1

5. The λmax for the absorption of FeSCN2+ in 0.1 M HNO3 is 450 nm (We get peak at 450 nm in wavelength vs absorbance graph plotted).