Determination of an Unknown Concentration of Potassium Manganate Using Colorimetry

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Determination of an Unknown Concentration of
Potassium Manganate using Colorimetry

Introduction
The purpose of this experiment is to conclude the concentration of an unknown solution using colorimetry to plot a calibration curve. Colorimetry measures the absorption of light at wavelengths within the visible region of the electromagnetic spectrum. It can be used to identify the unknown concentration of a solution in reference to a solution of a known concentration. When a solution appears coloured, you see the colour that has not been absorbed by the molecules. A light beam is passed through a sample inserted into a colorimeter, the light is split into two beams, one being absorbed by the sample, the other beam will pass through to a photocell which measure the amount of light absorbed. This figure is not measured in any unit but is an indication of the amount of light absorbed when referenced against other samples. Equipment

Potassium Manganate (100g/ml), distilled water, colorimeter, cuvettes, test tubes, test tube rack, burette, pipette. Part 1 - Determination of an Absorption Spectrum
An absorption spectrum will be created by measuring a sample of Potassium Manganate (100g/ml) against a range of wavelengths. The absorption spectrum will show how much light is absorbed at each wavelength.

Results
Wavelength (nm)| Absorption|
440| 0.35|
470| 0.48|
490| 1.40|
520| 2.00|
550| 1.93|
580| 0.88|
590| 0.37|
680| 0.19|

Part 2 – Determination of a Calibration Curve
The results indicate that the wavelength of maximum absorption is 520nm, this wavelength will be used to measure the absorption of a series of standard solutions. The standard solutions will be tested at the wavelength of maximum absorption as this wavelength would be the most sensitive to absorbance changes. As the amount of light absorbed is directly related to the concentration of the solution, the results can be used to determine the...
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