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

2. *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

3. 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

4. Question ???
What other purpose did HNO3 serve?

5. Answer:
Converts the manganese metal in steel to Mn2+, which then forms the permanganate ion with KIO4 as shown in the equation
2Mn IO H2O ↔ 2MnO IO H2O