Colorimetric Analysis: Manganese in Steel Essay Sample

The end of the experiment is to find the per centum of Mn in an unknown metal sample by agencies of colorimetric analysis.
First stock solution of KMnO4 with known concentration was diluted and so carried to spectrometer for analysis. The extremum with highest optical density was taken as ?max. Then the molar extinction coefficient is calculated by stop uping the value into the Beer-Lambert equation. Then the concentration of Mn2+ in unknown sample can be determined by scanning it in the spectrometer. 1

UV/VIS Spectrophotometry is used to find the soaking up or transmittal of UV/VIS visible radiation ( 180 to 820 nanometers ) by a sample. A spectrometer is used in the procedure. Inside a spectrometer visible radiation from a beginning is separated into narrow sets by wavelength. base on balls through the sample and so measured by the sensor. 2 In this experiment UV/VIS Spectrophotometry is used to find the optical density of MnO4- ion in the solution.

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Beer-Lambert jurisprudence provinces that optical density is relative to the concentration of the absorbing species. The equation is A=?bC. where A is the optical density. B is the way length. ? is the molar extinction coefficient and C stands for concentration. 2 In the experiment with the optical density of MnO4- ion in stock solution determined by UV Vis spectrophotometry in portion A and the optical density in unknown sample was determined in portion B. the concentration of Mn2+ can be calculated.

There was no alteration in the experiment. 1
Consequences and Discussion ( Sample # 2061 )

Part A
Dilution of KMnO4
10mL transferred to 100mL volumetric flask: 9. 9958mL ten 0. 003998M/100mL

10mL transferred to 100mL volumetric flask: 9. 9958mL ten 0. 003998M/100mL

20mL transferred to 100mL volumetric flask: 9. 9958mL ten 2x 0. 02M/100mL 20mL transferred to 100mL volumetric flask: 9. 9958mL ten 2x 0. 02M/100mL

The wavelength used was 526nm.
?=A/bC= 0. 935455/1?0. 00039963=2340. 8027 L mol?1 cm?1

Part B
Half-cell equations:
8H2O + 2Mn2+ —- & gt ; 2MnO4- +16 H+ +10e-
10e- +10H++ 5IO4—– & gt ; 2MnO4- +5IO3-+6H+
Internet balanced redox equation:
3H2O+ 2Mn2++5IO4—– & gt ; 2MnO4-+5IO3-+6H+
Calculation for KIO4:
1g x2 % =0. 02g

Molar mass of Mn2+=54. 938g/mol
nMn2+=0. 02/54. 938=3. 64046E-4mol
nKIO4=nMn2+ x2/5=9. 10115E-4mol
mKIO4=9. 10115E-4 x230. 00037=0. 2093g
Calculation for Unknown:
C=A/b ?=0. 462799/1?2340. 8027=1. 977E-4M
n=CV=1. 977E-4 ten 0. 25L=4. 9425E-5 mol
m=4. 9425E-5 x54. 938=2. 7153E-3g
Mass of unknown:0. 9629g
% Mn=2. 7153E-3/0. 9629 x100 % =0. 282 %

Overall drumhead inquiries:
1. Harmonizing to Beer’s jurisprudence. the optical density is dependent on the way length of the cuvette. Thus the value of ascertained optical density will be lower if 1mm cell is used. The molar extinction coefficient is an intrinsic belongings. which means it would non alter when the way length alterations. 2. No the consequence would be less accurate. The alteration in optical density around the highest extremum is minimized therefore the value derived from the highest extremum is the most accurate and closest to the true value. Decision

In portion A. by scanning the stock KMnO4 solution. the highest extremum of soaking up was found to be 526nm with optical density of 0. 935455. The molar extinction coefficient for Mn2+ was so deliberate 2340. 8027 L mol?1 cm?1. Then by scanning the sample solution at the wavelength 526nm. the optical density was found to be 0. 462799 and the concentration of Mn2+ in the sample was calculated to be 1. 977E-4M. Thus the per centum of Mn2+ in the sample was calculated 0. 282 % . There are several possible beginnings of mistake in the experiment including mistake in readings of pipette. taint of solution and sample may non wholly fade out. Mention

1. Dinging. Z. Maslen. R ; Stillman. M ; Yeung. K. Chemistry 2272 Laboratory Manual ; 2012 Ed ; Dept. of Chemistry. London. ON. 2012-2013 ; p 6. 1-6. 5. 2. Harris. C. H. Quantitative Chemical Analysis. 8th erectile dysfunction. ; W. H. Freeman and Company: New York. 2010