Lab chm 261

CHM 260 LAB REPORT

EXPERIMENT NO.

:

2

TITLE OF EXPERIMENT

:

UV-VIS DETERMINATION OF AN UNKNOWN CONCENTRATION KMNO4 SOLUTION.

PREPARED BY

:

MUSTAFIDZUL BIN MUSTAPHA

STUDENT NUMBER

:

2012561259

EXPERIMENT DATE

:

30/06/2015

SUBMISSION DATE

:

21/08/2015

LECRURER NAME

:

NAZWA JON

TITLE UV-Vis determination of an unknown concentration KMNO4 solution.

OBJECTIVE a) To determine the maximum wavelength of potassium permanganate. b) To plot the calibration curve of potassium permanganate c) To determine the concentration of an unknown solution of potassium permanganate.

INTRODUCTION UV-Vis spectra can be used to detect for the presence of absorbing functional groups or chromophores. UV-visible spectroscopy is a valid, simple and cost effective method for determining the concentration of absorbing species if applied to pure compounds, and used with the appropriate standard curve. A standard curve relating absorbance to concentration can be developed for any compound, and used to determine the concentration of samples containing the same compound. By using this UV-Vis Spectrophotometer, we can find inorganic aborbing species such as transition element ions, lanthanides and actinides as well as inorganic complexes or charge transfer complexes. The UV-Vis Spectrophotometer can be used for wavelength range of 180nm to 780nm as it emit both Visible and UV light.

INSTRUMENTS UV-Vis Spectrophotometer.

APPARATUS Beaker, burette, glass rod, 100 ml volumetric flask, dropper.

CHEMICALS Potassium permanganate (KMNO4)

PROCEDURE Preparation of the KMnO4 Standard Solutions 1

0.01 g of KMnO4 were accurately weighted and transfered into a beaker. The solid KMnO4 was then dissolved with distilled water.

2

The dissolved KMnO4 was diluted using 100mL volumetric flask and labelled as ‘100ppm’.

3

From the ‘stock’, 5mL of solution was pipetted and diluted again in 100mL. The solution was labelled as 5 ppm

4

The step 3 was repeated for 10 ppm,15 ppm and 20 ppm.

Preparation Of An Unknown 1

From the ‘stock’, an unknown volume was pipetted and diluted into 100mL volumetric flask.

2

The unknown sample was transfered into a beaker and labelled as “unknown”

QUESTIONS

1. Why is glass not suitable cell material for use in UV spectroscopy? Because glass will absorb the UV light, thus, making the absorbance reads both glass and sample measurement.

2. State one advantage of using the UV-Vis Spectrophotometer compared to a Spectronic-20 for this analysis. UV-Vis Spectrophotometer will directly plot us the graph compared to Spectronic20 which we have to plot the graph ourselves.

DISCUSSION From the experiment, we are able to determine the maximum wavelength of the Pottasium Peranganate, KMnO4 and to plot the calibration curve of KMnO4. We also have determine the concentration of an unknown solution of KMnO4. KMnO4 absorbs strongly in the visible range of wavelength between 500 and 550nm on different uv-visible spectrophotometers, it has been reported as having its wavelength of maximum absorption (λmax ) of normal wavelength as 525nm using spectronic 20, 522nm and Robert Bohman in 2006 reported his work as 520nm using perkins-elmer. At first, in this experiment, an initial permanganate stock solution is prepared and the solutions to be measured that are 5 ml, 10 ml, 15 ml, 20 ml and also unknown solution are diluted from a dilution of the stock. Once the absorbance value are taken, Beer’s law plot for KMnO4 is generated and the concentration of unknown solution can be determined. We used 15ml of KMnO4 stock solution for unknown solution in this experiment. UV-Vis spectroscopy has been used to do this experiment. Absorption in UV-Vis is mainly a study of molecules and their electronic transitions. In this experiment, a series of samples and unknown of inorganic complex had been prepared. The inorganic complex used was KMnO4. The absorption process of the complex is where the electron jumps from an orbital mostly centered on the ligand to an orbital mostly centered on the metal ion. The absorbance can be calculate using Beer’s Law: A  bc

A is the absorbance of light by the sample, b is the path length of the light (in cm), c is concentration (in molarity) and ε is a proportionality constant called the molar extinction coefficient (expressed in mol-1cm-1). After finding the λmax from the UV-Vis, the Beer’s Law graph was plotted for KMnO4 and thus the concentration of the unknown sample can be determine. The correlation coefficient has 0.999981which we get the accurate reading.

CONCLUSION The λmax for this experiment is 526.65 nm and the correlation coefficient is 0.999981.

REFERENCE

1.

Bohman, R. (2006, November 4). Ultraviolet/Visible (UV – Vis) Spectroscopy of potassium permanganate.

2.

Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch (2004). Fundamentals of Analytical Chemistry. 8th Edition.