In your own words, explain why the equilibrium concentration of FeSCN^2+ is know
ID: 1011140 • Letter: I
Question
In your own words, explain why the equilibrium concentration of FeSCN^2+ is known for the solutions in of the lab but not for the solutions in. Also describe how this is experimentally achieved and what assumptions are being made. Calculate the equilibrium concentration of FeSCN^2+ that is expected in each of the solutions listed in of the experimental procedure (blank and solutions 1-5). and units. Explain why HNO_3 is used to dilute each of the solutions in rather than distilled water. The blank solution used to calibrate the spectrophotometer is a solution of Fe(NO_3)3 and HNO_3. Why is this solution used rather than distilled water to perform the calibration? Look up and provide a brief explanation of what is meant by instrument drift. Explain how instrumental drift could affect the results of this experiment. Properly cite your reference source(s) for this information using ACS Style Guide formatting and state why you believe this is a reputable technical source. All waste for this lob should be collected in the liquid waste containers and disposed of properly. the concentrations of Fe(NO_3)_3 and KSCN solutions are different in and of this lab.Explanation / Answer
1. In part A, the equilibrium concentrations of FeSCN2+ would be equal to the concentration of SCN- in solution. SCN- is used as the limiting reagent and Fe3+ is in excess. So all SCN- would form the complex.
2. Calculations for equilibrium concentration of FeSCN2+
Blank A : 0 M
Std. solution 1 : [FeSCN]2+ = 5 x 10^-4 M x 5 drops x 0.05 ml/75 drops x 0.05 ml = 3.33 x 10^-5 M
Std. solution 2 : [FeSCN]2+ = 5 x 10^-4 M x 10 drops x 0.05 ml/75 drops x 0.05 ml = 6.66 x 10^-5 M
Std. solution 3 : [FeSCN]2+ = 5 x 10^-4 M x 20 drops x 0.05 ml/75 drops x 0.05 ml = 1.33 x 10^-4 M
Std. solution 4 : [FeSCN]2+ = 5 x 10^-4 M x 30 drops x 0.05 ml/75 drops x 0.05 ml = 2 x 10^-4 M
Std. solution 5 : [FeSCN]2+ = 5 x 10^-4 M x 45 drops x 0.05 ml/75 drops x 0.05 ml = 3 x 10^-4 M
3. HNO3 helps keep the Fe3+ in this form and not in the reduced Fe2+ form.
4. A solution of Fe(NO3)3 and HNO3 is used so that any net absorption due to Fe ions are cancelled well from the actual reading.
5. Instrument drift is a sow change in response with time. If we have a instrument drift in our measurement the data collected would not be easily averaged and thus induces an error.