Absorption spectroscopy ; Determination of Mn in steel.
Absorbance spectroscopy is a form of molecular spectroscopy.this method is used as an analytical chemistry tool.it can be usedin determining if a certain commodity might be present in smme sample.it also measures the quantity of the sample in place.when calculatingthe concentration of substance available,we use beers law ,through measuring the absorbance,in beer lambert law,we have alinear relationship between,absorbance,concentration,molar absorption coefficient and also optical coeffient of a solution.below is beers law eqoution.
A=eCl
A refers to absorbance
E refers to molar absorption coefficient
C refers to molar concentration
L refers to the optical path length used in experiment.
Measure of how strong
an absorber the sample is at a certain wavelength of ight is known as molar absorption coefficient.its a property that is dependent on sample.concentration refers to moles of sample which is dissolved in 1000cm3.path length refers to be length of cuvette used in measurement of absorbance in the spectrometer.the common typical length is usually 1cm.from the experiment done,on absoption spectrumof permanganate ion and its calibration,w obtained a linea curve.absorption spectrum of one of its standard was used to determine the wavelength of maximum absorption.the wavelength was found to be 515nm.
Calculation of molar extinction coefficient from the slope of the graph.
Step one is to plot a graph of absorbance against concentration.
(0.00004 – 0.00006)/(0.954 – 1.424)
=-0.00002/-0.47
=0.0000425532
Step 3 is to divide the slope with the depth of cuvette to get molar absorptivity.molar absorptivity is also known as molar extinction coefficients.
=slope/optical length
=0.0000425532/1
=0.0000425532Mol/l-1 /CM-1
Colorimetric determination of manganese content of steel
Manganese content of steel is slightly lower than one per cent.therefore,its not easy to quantitavely analyse manganese in a substance withi high amount of iron using chemical techniques.due to that ,we use calorimeter in order to get accuate and fine results.it involves dissolving the steel in nitric acid .Mn ions are thus oxidised to mn22+ ions.below is the equition of the rection taking place.
Mn + 2NO-3 + 8H+ 3Mn2+ + 2NO + 4H2O
Nitric acid is removed in order to prevent it from reacting with periodate which will later lead to oxidation of manganese ions to permanganate ions.therefore, boiling the samle and adding a cpmpond known as ammonium persulfate will help in eradication of NO.In order to prevent interferaance of ferric iron,phosphoric acid is added to the sample. A complex is thus forms at the end of the experiment.
Calculation of concentration of MNO4 is done as shown below.
Y = MX + C
M Is the gradient, and C is the Y Intercept
Slope of the graph was found to be 0.00004
The Y = 23820x and C = 0 in our case.X intercept is equal to negative y intercept divided by the slope.therefore in our case,it is
= ( -23820X /0.00004)
= -5.955 ppm.therefore the concentration of Mn in the sample of steel measured is 5.5955ppm.
Next step is to calculate amount of Mn which was in the samole of steel used.steel was diluted to 250ml after being grounded.10 ml of the solution was then taken and diluted to make to 100ml.
5.955ppm*(0.1/0.01)*0.250 =14.8875mg of Mn
Percentage mass of steel sample is (1.48875*10-3) / (0.5)*100
=0.29775%
5.955ppm*(0.1/0.02)*0.25=7.44375mg of Mn
Percentage mass of steel sample is (7.44375*10-3)/(0.5)*100
=1.48875%
Average=(0.29775+1.48875)/2=0.89325%.this value is slightly lower to 0.91% given on the tin.this shows that the experiment was not accurately done.