242959238-lab-ins-2.docx

CHM 260 LABORATORY REPORT

EXPERIMENT NO.

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TITLE OF EXPERIMENT

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. PREPARED BY

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STUDENT NUMBER

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EXPERIMENT DATE

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SUBMISSION DATE

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LECRURER NAME

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Title Objective

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

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

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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

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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.

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

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

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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.

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Data

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

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Solution

Concentration (ppm)

Absorbance

Standard 1

5

0.0683

Standard 2

10

0.1262

Standard 3

15

0.1963

Standard 4

20

0.2625

Unknown

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0.2151

The concentration of the unknown =

Results

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Questions

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16.5 ppm

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

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UV-Vis spectroscopy is based on selective absorption of electromagnetic radiation in the 180-780nm wavelength range. 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 bbe determine. The correlation coefficient must be 0.9999 to get accurate reading.

Conclusion

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The λmax for this experiment is 526.0nm and the correlation coefficient is 0.99928.

Reference

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