Iron is made from ore (usually hematite, Fe2O3) and carbon monoxide (CO) in a huge reactor called a blast furnace.

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CH 104 DETERMINATION OF MANGANESE IN STEEL THE
MANUFACTURE OF IRON

• Iron is made from ore (usually hematite, Fe2O3)
  and carbon monoxide (CO) in a huge reactor called
  a blast furnace.
• A charge of iron ore, coke (coal cake, C), and
  limestone (CaCO3) are added at the top of the
  furnace, and a blast of hot air is sent up from
  the bottom. The coke burns at 1,500 C to 2,000
  C and makes CO.
• 2C(s) O2(g) ? 2CO(g)
• As the charge falls, the CO(g) raises and causes
  the Fe2O3 to be reduced to Fe.
• Fe2O3(s) 3CO(g) ? 2Fe(l) 3CO2(g)
• The CaCO3 removes the impurities as slag.
• CaCO3(s) ? CaO(s) CO2(g)
• CaO(s) SiO2(s) ? CaSiO3(l)
• Lime Sand ? Slag

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THE MANUFACTURE OF IRON

• The iron made by a blast furnace is called pig or
  cast iron.
• It is brittle and has approximately 4 C and
  smaller amounts of other impurities such as Mn,
  P, S, and Si.

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THE MANUFACTURE OF IRON

• A modern blast furnace produces nearly 10,000,000
  kg (11,000 tons) of pig iron per day.
• This pig iron is used to manufacture steel.

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THE MANUFACTURE OF STEEL

• Steel is refined Fe that has less than 1.7 C.
  This process has 3 requirements.
• First, the approximately 4 C in pig iron is
  lowered to less than 1.7 C.
• Second, the Mn, P, S, and Si impurities from pig
  iron are removed as slag.
• Third, alloying elements, such as Cr, Mn, Mo, Ni,
  V, and W, are added to give the steel its desired
  properties.

• Approximately 800 million tons of steel is
  produced each year. That is, over 250 pounds of
  steel is made for each person on Earth each year.

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THE MANUFACTURE OF STEEL

• Molten pig iron from the blast furnace is
  typically poured into a basic oxygen furnace and
  made into steel.
• Some of the C in pig iron is oxidized with O2(g)
  and removed as CO(g) and CO2(g).
• The inorganic impurities in pig iron are oxidized
  with O2(g), reacted with basic oxides, and
  removed as slag.
• P4(l) 5O2(g) ? P4O10(l)
• 6CaO(s) P4O10(l) ? 2Ca3(PO4)2(l)
• Basic Oxide Acidic Oxide ? Slag

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THE MANUFACTURE OF STEEL

• Finally, alloying elements, such as Cr, Mn, Mo,
  Ni, V, and W, are added to give the steel its
  desired properties.
• For example, Cr, Mo, and Ni give corrosion
  resistance to stainless steels.
• Manganese (Mn) makes steel easier to deform at
  high temperatures. It is added to help the
  rolling and forging steps of steel production.
• In todays experiment you will measure the Mn
  content of steel.
• You will be graded on the accuracy of your result.

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SAMPLE PREPARATION

• Tare a 250 mL Erlenmeyer flask.
• Accurately weigh 0.3 g of steel to 3 significant
  digits into this flask. For example, your sample
  might weigh 0.306 g. Record this mass in your
  data sheet.
• Perform this step in a FUME HOOD. CAREFULLY add
  50 mL of 6 M (dilute) nitric acid (HNO3). If
  necessary, carefully heat the reaction mixture on
  a hot plate until all the steel is dissolved.
  The purpose of this step is to dissolve the
  manganese.
• Mn(s) 4HNO3(aq) ? Mn2(aq) 2NO3(aq)
  2NO2(g) 2H2O(l)

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SAMPLE PREPARATION

• Perform this step in a FUME HOOD. CAREFULLY add
  1 g of ammonium peroxydisulfate ((NH4)2S2O8) and
  boil gently for 10 minutes. The purpose of this
  step is to remove any color from
  carbon-containing compounds.
• 2S2O82(aq) C(aq) 2H2O(l) ? CO2(g)
  4SO42(aq) 4H(aq)
• Perform this step in a FUME HOOD. CAREFULLY add
  0.1 g of sodium hydrogen sulfite (NaHSO3) and
  heat for another 5 minutes. The purpose of this
  step is to remove any color from permanganate ion
  (MnO4).
• 5HSO3(aq) 2MnO4(aq) H(aq) ? 2Mn2(aq)
  5SO42(aq) 3H2O(l)
• Perform this step in at your bench. You are done
  using the fume hood. Cool and dilute the
  solution to exactly 100 mL in a volumetric flask.
  Shake well to mix.

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SAMPLE PREPARATION

• Pipet three 25 mL aliquots of the sample into
  small beakers. Treat these aliquots by adding
  the following reagents
• Boil aliquots 1 and 2 gently for 5 minutes and
  cool.
• Dilute each of the 3 aliquots to 100 mL in
  volumetric flasks.
• The nearly colorless manganese(II) ion (Mn2) is
  oxidized to the purple permanganate ion (MnO4).
• 5IO4 2Mn2 3H2O ? 2MnO4 5IO3 6H
• You will measure the concentrations of MnO4 in
  these 3 aliquots with a spectrophotometer at 525
  nanometers (nm).

Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g
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SAMPLE ANALYSIS BY STANDARD ADDITION

• The standard addition method is used eliminate or
  reduce interference from the sample matrix. It
  has 3 steps.
• First, the signal from a sample is measured.
• Second, the signal from a mixture of this sample
  and a known amount of standard is measured.
• Third, these data are used to calculate the
  concentration of analyte in the sample.

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SAMPLE ANALYSIS BY STANDARD ADDITION
Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g

• Dilute each of the 3 aliquots to 100 mL in
  volumetric flasks.
• What is the purpose of Aliquot 1?
• All the Mn is from the sample. All this Mn is
  oxidized to MnO4. Aliquot 1 is used to measure
  the concentration of Mn in the sample.
• What is the purpose of Aliquot 2?
• All the Mn is from the sample and the standard.
  All this Mn is oxidized to MnO4. Aliquot 2 is
  used to measure the total concentration of Mn in
  the sample and in the standard.
• What is the purpose of Aliquot 3?
• All the Mn is from the sample. None of this Mn
  is oxidized to MnO4. Aliquot 3 is used to set
  the spectrophotometer to 0 absorbance (100
  transmittance). This accounts for any color from
  the sample not from MnO4. Therefore, aliquot 3
  is a blank and it is used to remove interferences.

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SAMPLE ANALYSIS BY STANDARD ADDITION

• Applying Beers Law to this experiment
• A abc
• A absorbance
• a the absorptivity constant for MnO4
• b the path length of the sample cell
• c the concentration of MnO4 in the sample cell
• Since a (absorptivity) and b (path length) are
  constant for a given wavelength and a given
  sample cell, A (absorbance) is directly
  proportional to c (concentration)

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SAMPLE ANALYSIS BY STANDARD ADDITION

• Furthermore, absorbances are additive
• Atotal A1 A2 A3
• The absorbance of aliquot 1 (Aaliquot1) is caused
  by the Mn from the sample being oxidized to
  MnO4. Therefore, the absorbance of
• aliquot 1 (Aaliquot1) equals the absorbance of
  the sample (Asample).
• A1 Aaliquot1 Asample
• The absorbance of aliquot 2 is caused by the Mn
  from the sample and standard being oxidized to
  MnO4. Therefore, the absorbance of
• aliquot 2 (Aaliquot2) equals the absorbance of
  the sample (Asample) plus the absorbance of the
  standard (Astandard).
• A2 Aaliquot2 Asample Astandard

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SAMPLE ANALYSIS BY STANDARD ADDITION

• Solving for the concentration of Mn in the sample
  cell
• cstandard is the concentration of Mn in the
  sample cell. It is NOT the concentration of Mn
  in the bottle of Standard Mn.
• csample is the concentration of Mn in the sample
  cell. It is NOT the concentration of Mn in steel.

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SAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved,
  diluted to 100.0 mL, and prepared as follows.
• Afterwards, each of the 3 aliquots were diluted
  to 100.0 mL. The Standard Mn solution contained
  102.6 mg of Mn / L. Aaliquot1 equaled 0.152.
  Aaliquot2 equaled 0.376.
• What is cstandard?
• Again, cstandard is the concentration of Mn in
  the sample cell. It is NOT 102.6 mg of Mn / L.

Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g
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SAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved,
  diluted to 100.0 mL, and prepared as follows.
• Afterwards, each of the 3 aliquots were diluted
  to 100.0 mL. The Standard Mn solution contained
  102.6 mg of Mn / L. Aaliquot1 equaled 0.152.
  Aaliquot2 equaled 0.376.
• What is csample?
• Again, csample is the concentration of Mn in the
  sample cell. It is NOT the concentration of Mn
  in steel.

Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g
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SAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved,
  diluted to 100.0 mL, and prepared as follows.
• Afterwards, each of the 3 aliquots were diluted
  to 100.0 mL. The Standard Mn solution contained
  102.6 mg of Mn / L. Aaliquot1 equaled 0.152.
  Aaliquot2 equaled 0.376.
• How many grams of Mn are in this steel sample?

Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g
18
SAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved,
  diluted to 100.0 mL, and prepared as follows.
• Afterwards, each of the 3 aliquots were diluted
  to 100.0 mL. The Standard Mn solution contained
  102.6 mg of Mn / L. Aaliquot1 equaled 0.152.
  Aaliquot2 equaled 0.376.
• What is the Mn in this steel?

Aliquot Concentrated H3PO4 Standard Mn KIO4
1 2 3 3 to 5 mL 3 to 5 mL 3 to 5 mL 0.00 mL 5.00 mL 0.00 mL 0.4 g 0.4 g 0.0 g
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SAFETY

• Give at least 1 safety concern for the following
  procedure.
• Using acids (HNO3 and H3PO4), oxidizing agents
  (HNO3, (NH4)2S2O8, KIO4, and KMnO4), and reducing
  agents (Mn2 and NaHSO3).
• These are irritants. Wear your goggles at all
  times. Immediately clean all spills. If you do
  get either of these in your eye, immediately
  flush with water.
• Your laboratory manual has an extensive list of
  safety procedures. Read and understand this
  section.
• Ask your instructor if you ever have any
  questions about safety.

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SOURCES

• Harris, D.C. 1999. Quantitative Chemical
  Analysis, 5th ed. New York, NY W.H. Freeman
  Company.
• McMurry, J., R.C. Fay. 2004. Chemistry, 4th ed.
  Upper Saddle River, NJ Prentice Hall.
• Merriam-Webster, Inc. 1987. Websters 9th New
  Collegiate Dictionary. Springfield, MA
  Merriam-Webster, Inc.
• Petrucci, R.H. 1985. General Chemistry Principles
  and Modern Applications, 4th ed. New York, NY
  Macmillan Publishing Company.
• San José State University. 2007. Photometric
  Determination of Manganese in Steel. Available
  http//www.sjsu.edu/faculty/chem55/55phot.htm
  accessed 22 February 2007.
• Specialty Steel Industry of North America. 2006.
  SSINA Stainless Steel About. Available
  http//www.ssina.com/index2.html accessed 12
  October 2006.
• Tro, NJ. 2008. Chemistry, A Molecular Approach.
  Upper Saddle River, NJ Prentice Hall.