AS2 DETERMINATION OF MANGANESE IN STEEL Last Revised: May 2015
1. REAGENTS & EQUIPMENT 1.1 steel drillings, Mn around 0.5‐1.5% 1.2 5 M HNO3 1.3 ammonium persulfate (solid) 1.4 concentrated phosphoric acid 1.5 potassium periodate (solid) 2. PROCEDURE 2A. Solution preparation 2.1
Obtain three steel standards of known Mn content and a sample. 2.2
Weigh accurately approximately 0.20 g of each of the standards into 250 mL conical beakers. 2.3
In duplicate, weigh accurately approximately 0.20 g of the sample into 250 mL conical beakers. 2.4
Weigh out about 0.2 g of one of the steels to act as a blank. The blank should be subjected to the same treatment as the standards and sample EXCEPT THE ADDITION OF POTASSIUM PERIODATE. 2.5
To each beaker add 5 M HNO3 (25 mL by measuring cylinder). 2.6
Heat gently on the hot plate in a hood. 2.7
After the steels have dissolved, cover with the watch glass and boil for 2 minutes to remove oxides of nitrogen (no more brown gas is evolved). A black residue of carbides may remain at this stage. 2.8
Remove the beakers from the heat, cool slightly and carefully add ammonium persulfate (1 g) into each beaker. 2.9
Boil gently for 10‐15 minutes. 2.10 Dilute each solution to about 50 mL and add concentrated phosphoric acid (15 mL) and potassium periodate (0.3 g) (not in the blank). 2.11 Boil gently for about 3 minutes to convert Mn (II) to purple permanganate. Cool below boiling and then add an additional 0.2 g portion of potassium periodate. Boil for another 1‐2 minutes. 2.12 Transfer each of the solutions to 250 mL volumetric flasks and make up to the mark with distilled water. 2B. Analysis 2.13 Set up the instrument to scan the visible region. What wavelength range is this? What cell should you choose? 2.14
2.15
Zero (baseline) the instrument with the blank. Record the spectrum of one of the standards. Decide on a suitable wavelength for quantitative measurements. Set the instrument to this wavelength and re‐zero (if necessary). Measure the absorbance of each solution. 2.16
2.17
REPORT Calculations 
calculate the mg of Mn in each standard 
calculate the concentration of each standard in mg/L 
plot a calibration graph of absorbance against mg/L Mn 
determine the concentration of Mn in the samples 
for each sample individually: o calculate the mass of Mn in the 250 mL flask o calculate the %w/w of Mn 
calculate the average %w/w Mn Discussion 
explain the reasons for the following preparation steps: o addition of nitric acid o boiling to remove oxides of nitrogen o addition of ammonium persulfate o addition of potassium periodate o not adding periodate to the blank 
explain why the standards were prepared using steels rather than from 1000 mg/L Mn standard 
compare this method for Mn in steel with analysis by AAS analysis of the same sample Questions 1.
What sample preparation step in this procedure would not be required if analysing this sample by AAS? 2.
List the important interferences (other than Cr) in this determination of Mn in steels. Outline how they are minimised. 3.
What is the function of Mn in steel? What levels of Mn are typically added to steels? There is a guide to this Exercise, including help with the calculations, on the website. AS2 p2 AS2. MN IN STEEL
RESULTS SHEET
%Mn Mass (g)
Standard 1 Standard 2 Standard 3 Sample 1 mass (g) Sample 2 mass (g) Abs. Standard 1 Standard 2 Standard 3 Sample 1 Sample 2