Rainey_Experiment 3

Rainey_Experiment 3 - Experiment 3: Spectroscopic...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 3: Spectroscopic Determination of Formulas and Stability Constants of Complex Ions Author: Ben Rainey Group 2 Section 3, T 2:00 PM – 5:00 PM Partner: Ben Huffer November 9, 2010 Abstract : In this experiment, the two main scientific goals were to determine the formula of and to determine the stability constant of a metal-ligand complex. The complex consisted of copper and iminodiacetic acid (IDA). To accomplish these goals a Shimadzu UV/Vis and the method of continuous variations was used. The hypothetical absorbencies were generated by analyzing the absorbance near the extreme mole fraction values. Linear regression was used to determine absorbencies that should ideally model hypothetical behavior. These hypothetical absorbencies were then compared with measured absorbencies. It was found that copper complexes with IDA in a 1:1 ratio. The measured absolute stability constant was determined to be 3.66*10 10 ±6.14*10 9 M -1 . The measured absolute stability constant had an uncertainty of 16.8%. The value obtained for the absolute stability constant was in agreement with the literature value of 4*10 10 M -1 with a 25% uncertainty. I. Introduction Spectroscopy is one method used to determine the composition of ions formed in a solution and to determine the stability constant of the ion of interest. In order to find the composition of a metal-ligand complex formed in solution, the method of continuous variations can be utilized. One can continuously vary the concentrations of each of the components making up the metal-ligand complex. The metal-ligand complex under
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Experiment 3: Spectroscopic Determination of Formulas and Stability Constants of Complex Ions study in this experiment is the copper-IDA complex. By varying the concentrations of each of the metal-ligand components, while keeping the total solute concentration constant, and measuring the absorbance at each concentration combination, the chemical formula of the metal-ligand complex of interest can be determined. In order to obtain an accurate measure of the amount of metal-ligand complex present in each of the prepared solutions, one must set the spectrometer to a wavelength where the complex absorbs light strongly and the metal ion and the ligand do not. If one of the compounds used to make the complex absorbs light well at the wavelength of interest, a calibration can be obtained in order to determine the actual absorbance of the complex. If the absorbance of the metal-ligand complex is graphed against the mole fraction of the ligand, a convex-down curve is formed. Towards the extreme values of mole fraction of the ligand, linear trend lines can be formed. By extrapolating trend lines for both of the extreme values of mole fraction of ligand, the theoretical absorbance of the complex for a reaction that went to completion can be determined. The intersection of these extrapolated lines yields the theoretical mole fraction of ligand that corresponds to the maximum yield of the metal-ligand complex. The composition of the metal-ligand
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/08/2011 for the course CHEM 232 taught by Professor James during the Spring '11 term at Clemson.

Page1 / 9

Rainey_Experiment 3 - Experiment 3: Spectroscopic...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online