II.Procedure
A. Preparation and absorbance determination of standard solutions.

Weigh out 0.1389 grams of reagent grade KMn04 into a 250 mL volumetric flask. Dissolve in about 100 mL of distilled water.  Add 6 mL of concentrated H2S04· Dilute to the mark with distilled water. This will give a solution which has a concentration of 3.50 mM permanganate. By diluting this solution in 100 mL volumetric flasks, prepare 6 standard solutions whose concentrations span the range 0.4 mM to 0.04 mM. If exactly 0.1389 g of potassium permanganate is not weighed out, determine the actual concentration of the KMn04 solution and use this value in determining the concentrations of the standard solutions. Measure an absorption spectrum of permanganate solution in visible area. Make a Beer's Law plot for these  solutions at the maximum of absorption.  A = e C l Determine molar absorptivity  e of MnO4 - ion. B. Preparation and analysis of sample.  Dry your manganese ore sample 1 hour at about 110oC in the small oven in the instrumental analysis lab. Weigh out to the nearest tenth of a milligram a single sample of the ore weighing between 0.1 and 0.2 g. Transfer to a 250 mL Erlenmeyer flask and add 50 mL of 6M HN03. Place the Erlenmeyer on a steam bath and add dropwise 2 mL of 30% hydrogen peroxide. Allow all the foaming to subside. If all the MnO2 particles are not dissolved, a third mL of hydrogen peroxide may have to be added. When all the MnO2 particles have dissolved, and no foaming has occurred for 5 minutes, heat on the steam bath for several minutes to expel oxides of nitrogen. Your entire sample will  NOT dissolve due to silicate impurities found in all ore samples. These particles will be white or tan.  Cautiously add 1 g  of potassium peroxydisulfate (persulfate) and heat to about 85oC on the steam bath for about 10 minutes to oxidize carbon compounds and other reducing agents which might subsequently react with permanganate or periodate. The heating also destroys the excess peroxydisulfate.  Cool and transfer quantitatively to a 250 mL volumetric flask. Dilute to the mark and mix thoroughly. Pipette 2.5 mL portions into three 100 mL beakers, add to each 10-15 mL of water, 1 mL conc. sulfuric acid, and  5 mL of 85% H3P04. Cover the beakers with watch glasses. Two of these portions are to be duplicate samples in the colorimetric step, and the third is to serve as a blank, to compensate for color due to components other than manganese.  Add to each of the duplicate samples 0.3g of potassium metaperiodate, KIO4, heat to a gentle boil on a Bunsen burner and keep at the boiling temperature for 5 min with occasional stirring until the solution has turned purple, and not orange. After this 5 minutes of gentle boiling, add another 0.3 gm portion of potassium metaperiodate to each of the duplicate samples and boil gently for another 5 minutes. Do not add KIO4 to the 3rd sample, the blank.  Cool the samples. Transfer the duplicate samples and blank quantitatively to 100 mL volumetric flasks and dilute to the mark with distilled water and measure the absorbance as follows. Set the spectrophotometer to maximum wavelength. Fill the reference spectrophotometer cell with the blank solution. Fill the sample cell with one of the sample solutions. Read the absorbance of the sample vs. the blank from the spectrophotometer. Repeat using the second sample solution.  IV. Report A. Report the percentage of Mn in your ore sample to 3 significant figures.  B. Turn in your Beer's Law plot. Estimate standard deviation of blank and of your measurements. Estimate detection and determination limits of the procedure.