Chemistry

EXPERIMENT 11 UV/VIS Spectroscopy and Spectrophotometry: Spectrophotometric Analysis of Potassium Permanganate Solutions.

Outcomes

After completing this experiment, the student should be able to: 1. 2. 3. 4. Prepare standard solutions of potassium permanganate. Construct calibration curve based on Beer’s Law. Use Beer’s Law to determine molar absorptivity. Explain the fundamental principal behind spectrophotometric analysis

Introduction

Most analytical methods require calibration (a process that relates the measured analytical signal to the concentration of analyte, the substance to be analyzed). The three most common analysis methods include the preparation and use of a calibration curve, the standard addition method, and the internal standard method. In this experiment we will use spectrophotometry to prepare a calibration curve for the quantitative analysis of KMnO4.

Spectrophotometry

Spectrophotometry is a technique that uses the absorbance of light by an analyte (the substance to be analyzed) at a certain wavelength to determine the analyte concentration. UV/VIS (ultra violet/visible) spectrophotometry uses light in UV and visible part of the electromagnetic spectrum. Light of this wavelength is able to effect the excitation of electrons in the atomic or molecular ground state to higher energy levels, giving rise to an absorbance at wavelengths specific to each molecule. The complex formed between ASA and Fe3+ is intensely violet coloured, and therefore can be determined by spectrophotometry using the visible part of the electromagnetic spectrum. The human eye is able to “see’ light in the wavelength range 400-700 nm (nanometer or 10−9 m). To the human eye, wavelength appears as colour, as shown in the following table. Table: Correlation between wavelength, colour, and complementary colour Wavelength, nm 400-430 430-490 490-550 550-590 590-630 630-700 Colour Violet Blue Green Yellow Orange Red Complementary colour Yellow-green Yellow Purple Blue...