How do I go about this experiment? what are the appropriate glassware needed? wh

Question

How do I go about this experiment?
what are the appropriate glassware needed?
what is the proper instrumentation?
what is the procedure for finding Kc, including all required dilutions?

Experiment In this experiment the goal is to calculate the equilibrium constant for the reaction of iron (II) with thiocyanate to produce iron (IIl) isothiocyanate: Fe3+ + SCN Fe(NCs)2+ Fe(NCS)2+ is a deep blood red complex that absorbs light of approximately 460nm. Using spectroscopy and Beer's Law, the concentration of Fe(Ncs)2+ in solution can be determine. Recall, Beer's Law is given by concen where A is the absorbance, e is the molar absorbance coefficient, b is the path length, and c is the A plot of absorbance versus known analyte concentration will yield eb, which can be used to determine the concentration of the product at equilibriurm

Explanation / Answer

In this experiment, you will use a spectrophotometer to determine [Fe(NCS)2+] in the equilibrium mixtures. Instructions for use of the Spectronic 20D spectophotometer are attached. The spectrophotometer measures absorbance, the amount of light absorbed by the complex at a given wavelength. Beer’s law expresses the relationship between absorbance, A, and concentration of a colored species, c.A =bc.

Here, is a constant that depends on the wavelength of light and on the substance that is absorbing the light; b is the distance that the light travels through the sample of the absorbing substance.

The equilibrium constant expression Kc for reaction is: [Fe(NSC)2+]/[Fe3+][SCN-]=Kc

You need test tubes to prepare samples and cuvette to put sample in it to measure absorbance. Spectrometer is needed to measure absorbance.

This is a experiment of Absorbance Spectroscopy.

Fe(NCS)2+ is a deep blood red complex which absorbs light t 460 nm. Therefore, at this wavelength absorbance measurements will have the highest sensitivity to [Fe(NCS)2+]. In this experiment, you will measure the absorbance of all solutions at 460 nm.

In the first part of the experiment, you will determine the relationship between the absorbance and [Fe(NCS)2+] at 460 nm. You will do this by measuring the absorbance of three standard solutions, in which [Fe(NCS)2+] is known.

Once you have measured the absorbances of the standard solutions, you will plot the absorbances against the concentrations of Fe(NCS)2+on a graph, or “calibration curve”. The points on the calibration curve will fall on a straight line, which has a slope of b, the constant of proportionality between absorbance and concentration.

In the second part of the experiment, you will measure the absorbance of a different set of solutions, in which substantial amounts of both reactants and the product are present. You will use your calibration curve to convert the measured absorbance to the equilibrium concentration of Fe(NCS)2+ in each solution. From the initial concentrations of the reactants and the equilibrium concentration of the product, you will calculate the equilibrium constant for the reaction.

Procudure:

1. Obtain ~40 mL of Fe(NO3)3 solution in a small beaker. Do the same for ~25 mL NaSCN solution. And, ~ 20 mL HNO3.

2.Use 5 different clean, dry largetest tubes. Label them 1-5. Using a different pipet for each solution, pipet the following amounts of each reagent into the given test tube. (The HNO3 acts to prevent the degredation of the reagents and can be considered inert in this reaction.) Mix each solution thoroughly.

3. Record your observations.

4. Fill a spectrometer cuvette ~2/3 full with each of these solutions. Do the same for an HNO3 blank solution. Do not touch the faces of the cuvettes; handle them from the edges. Use a Kimwipe to clean the faces of the cuvettes before making any readings.

5. Proceed to the instrument room to make the absorbance measurements.

Observations:

1. Set-up a Table such as that below and calculate the Initial Concentration of [Fe3+]and [SCN-] for ech set:

2. Now use your Absorbance measurements to calculate [Fe(NCS)2+] for each set. Finally, calculate Kc for each set.

[Fe(NCS)2+] (M)

Result: Submit your final Kc Value.

S.NO Fe(NO3)3 0.002M NaSCN solution 0.002M HNO3 solution 1. 5 ml 1 ml 4 ml 2. 5 ml 2 ml 3 ml 3. 5 ml 3 ml 2 ml 4. 5 ml 4 ml 1 ml 5. 5 ml 5 ml 0 ml

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