Determining Manganese in Steel (EXP. K-4) Procedure

*Standard addition method to determine Mn and compensate for matrix effects (everything other than analyte) * Procedure: obtain steel sample and analytically weigh three samples place in 250 ml beakers add 50 ml 4F HNO3 (steel will dissolve) to each -Boil solution in the fume hood add 1 gram ammonium peroxodisulfate to each -boil for 15 minutes then cool (oxidize carbon in steel) transfer to 100 ml volumetric flasks and dilute to mark

For the first sample in 100 ml volumetric flask… transfer four 20 ml aliquots into 250 ml beakers 1st – 5 ml H3PO4 (compensate iron III present); this is also the blank 2nd – 5 ml H3PO4, .4 gram KIO4 (forms colored permanganate ion) 3rd – 5 ml H3PO4, .4 gram KIO4, 5 ml standard Mn 4th – 5 ml H3PO4, .4 gram KIO4, 10 ml standard Mn Boil for five minutes, cool, and transfer to 50 ml volumetric flasks and dilute to mark Measure absorbance at 525 nm of each aliquot For the second then the third samples in volumetric flaks, the same procedure is done as for the first sample

Question ??? What other purpose did HNO3 serve?

Answer: Converts the manganese metal in steel to Mn2+, which then forms the permanganate ion with KIO4 as shown in the equation 2Mn2+ + 5IO4- + 9H2O ↔ 2MnO4- + 5IO3- + 6H2O