• Iron is made from ore (usually hematite, FeIron is made from ore (usually hematite, Fe22OO33) and carbon monoxide ) and carbon monoxide

(CO) in a huge reactor called a (CO) in a huge reactor called a blast furnaceblast furnace..• A charge of iron ore, A charge of iron ore, cokecoke ( (cocoal caal cakeke, C), and limestone (CaCO, C), and limestone (CaCO33) are ) are

added at the top of the furnace, and a blast of hot air is sent up from 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.the bottom. The coke burns at 1,500° C to 2,000° C and makes CO.

2C2C(s)(s) + O + O2(g)2(g) → 2CO → 2CO(g)(g)

• As the charge falls, the COAs the charge falls, the CO(g)(g) raises and causes the Fe raises and causes the Fe22OO33 to be reduced to be reduced

to Fe.to Fe.

FeFe22OO3(s)3(s) + 3CO + 3CO(g)(g) → 2Fe → 2Fe(l)(l) + 3CO + 3CO2(g)2(g)

• The CaCOThe CaCO33 removes the impurities as removes the impurities as slagslag..

CaCOCaCO3(s)3(s) → CaO → CaO(s)(s) + CO + CO2(g)2(g)

CaOCaO(s)(s) + SiO + SiO2(s)2(s) → CaSiO → CaSiO3(l)3(l)

Lime + Sand → SlagLime + Sand → Slag

CH 104: DETERMINATION OF MANGANESE IN STEELCH 104: DETERMINATION OF MANGANESE IN STEEL

THE MANUFACTURE OF IRONTHE MANUFACTURE OF IRON

• The iron made by The iron made by a blast furnace is a blast furnace is called called pig or cast pig or cast ironiron..

• It is brittle and has It is brittle and has approximately 4% approximately 4% C and smaller C and smaller amounts of other amounts of other impurities such as impurities such as Mn, P, S, and Si.Mn, P, S, and Si.

THE MANUFACTURE OF IRONTHE MANUFACTURE OF IRON

• A modern blast furnace produces nearly 10,000,000 kg A modern blast furnace produces nearly 10,000,000 kg (11,000 tons) of pig iron per day.(11,000 tons) of pig iron per day.

• This pig iron is used to manufacture steel.This pig iron is used to manufacture steel.

THE MANUFACTURE OF IRONTHE MANUFACTURE OF IRON

• SteelSteel is refined Fe that has less than 1.7% C. This process is refined Fe that has less than 1.7% C. This process has 3 requirements.has 3 requirements.

• First, the approximately 4% C in pig iron is lowered to less First, the approximately 4% C in pig iron is lowered to less than 1.7% C.than 1.7% C.

• Second, the Mn, P, S, and Si impurities from pig iron are Second, the Mn, P, S, and Si impurities from pig iron are removed as slag.removed as slag.

• Third, Third, alloying elementsalloying elements, such as Cr, Mn, Mo, Ni, V, and W, , such as Cr, Mn, Mo, Ni, V, and W, are added to give the steel its desired properties.are added to give the steel its desired properties.

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

THE MANUFACTURE OF STEELTHE MANUFACTURE OF STEEL

• Molten pig iron from the blast furnace is typically poured into a Molten pig iron from the blast furnace is typically poured into a basic basic oxygen furnaceoxygen furnace and made into steel. and made into steel.

• Some of the C in pig iron is oxidized with OSome of the C in pig iron is oxidized with O2(g)2(g) and removed as CO and removed as CO(g)(g)

and COand CO2(g)2(g)..

• The inorganic impurities in pig iron are oxidized with OThe inorganic impurities in pig iron are oxidized with O2(g)2(g), reacted with , reacted with

“basic oxides”, and removed as slag.“basic oxides”, and removed as slag.

PP4(l)4(l) + 5O + 5O2(g)2(g) → P → P44OO10(l)10(l)

6CaO6CaO(s)(s) + P + P44OO10(l)10(l) → 2Ca → 2Ca33(PO(PO44))2(l)2(l)

Basic Oxide + Acidic Oxide → SlagBasic Oxide + Acidic Oxide → Slag

THE MANUFACTURE OF STEELTHE MANUFACTURE OF STEEL

• Finally, alloying elements, such as Cr, Mn, Mo, Ni, V, and Finally, alloying elements, such as Cr, Mn, Mo, Ni, V, and W, are added to give the steel its desired properties.W, are added to give the steel its desired properties.

• For example, Cr, Mo, and Ni give corrosion resistance to For example, Cr, Mo, and Ni give corrosion resistance to stainless steels.stainless steels.

• Manganese (Mn) makes steel easier to deform at high Manganese (Mn) makes steel easier to deform at high temperatures. It is added to help the rolling and forging temperatures. It is added to help the rolling and forging steps of steel production.steps of steel production.

• In today’s experiment you will measure the Mn content of In today’s experiment you will measure the Mn content of steel.steel.

• You will be graded on the accuracy of your result.You will be graded on the accuracy of your result.

THE MANUFACTURE OF STEELTHE MANUFACTURE OF STEEL

• Tare a 250 mL Erlenmeyer flask.Tare a 250 mL Erlenmeyer flask.

• Accurately weigh 0.3 g of steel to 3 significant digits into Accurately weigh 0.3 g of steel to 3 significant digits into this flask. For example, your sample might weigh 0.306 g. this flask. For example, your sample might weigh 0.306 g. Record this mass in your data sheet.Record this mass in your data sheet.

• Perform this step in a FUME HOOD. CAREFULLY add 50 Perform this step in a FUME HOOD. CAREFULLY add 50 mL of 6 M (dilute) nitric acid (HNOmL of 6 M (dilute) nitric acid (HNO33). If necessary, carefully ). If necessary, carefully

heat the reaction mixture on a hot plate until all the steel is heat the reaction mixture on a hot plate until all the steel is dissolved. The purpose of this step is to dissolve the dissolved. The purpose of this step is to dissolve the manganese.manganese.

MnMn(s)(s) + 4HNO + 4HNO3(aq)3(aq) → Mn → Mn2+2+(aq)(aq) + 2NO + 2NO3–3–

(aq)(aq) + 2NO + 2NO2(g)2(g) + 2H + 2H22OO(l)(l)

SAMPLE PREPARATIONSAMPLE PREPARATION

• Perform this step in a FUME HOOD. CAREFULLY add 1 g of Perform this step in a FUME HOOD. CAREFULLY add 1 g of ammonium peroxydisulfate ((NHammonium peroxydisulfate ((NH44))22SS22OO88) and boil gently for 10 minutes. ) and boil gently for 10 minutes.

The purpose of this step is to remove any color from carbon-The purpose of this step is to remove any color from carbon-containing compounds.containing compounds.

2S2S22OO882–2–

(aq)(aq) + C + C(aq)(aq) + 2H + 2H22OO(l)(l) → CO → CO2(g)2(g) + 4SO + 4SO442–2–

(aq)(aq) + 4H + 4H++(aq)(aq)

• Perform this step in a FUME HOOD. CAREFULLY add 0.1 g of sodium Perform this step in a FUME HOOD. CAREFULLY add 0.1 g of sodium hydrogen sulfite (NaHSOhydrogen sulfite (NaHSO33) and heat for another 5 minutes. The ) and heat for another 5 minutes. The

purpose of this step is to remove any color from permanganate ion purpose of this step is to remove any color from permanganate ion (MnO(MnO44

––).).

5HSO5HSO33––

(aq)(aq) + 2MnO + 2MnO44––

(aq)(aq) + H + H++(aq)(aq) → 2Mn → 2Mn2+2+

(aq)(aq) + 5SO + 5SO442–2–

(aq)(aq) + 3H + 3H22OO(l)(l)

• Perform this step in at your bench. You are done using the fume hood. 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. Cool and dilute the solution to exactly 100 mL in a volumetric flask. Shake well to mix.Shake well to mix.

SAMPLE PREPARATIONSAMPLE PREPARATION

• Pipet three 25 mL aliquots of the sample into small beakers. Treat Pipet three 25 mL aliquots of the sample into small beakers. Treat these aliquots by adding the following reagents:these aliquots by adding the following reagents:

• Boil aliquots 1 and 2 gently for 5 minutes and cool.Boil aliquots 1 and 2 gently for 5 minutes and cool.

• Dilute each of the 3 aliquots to 100 mL in volumetric flasks.Dilute each of the 3 aliquots to 100 mL in volumetric flasks.

• The nearly colorless manganese(II) ion (MnThe nearly colorless manganese(II) ion (Mn2+2+) is oxidized to the purple ) is oxidized to the purple permanganate ion (MnOpermanganate ion (MnO44

––).).

5IO5IO44–– + 2Mn + 2Mn2+2+ + 3H + 3H22O → 2MnOO → 2MnO44

–– + 5IO + 5IO33–– + 6H + 6H++

• You will measure the concentrations of MnOYou will measure the concentrations of MnO44–– in these 3 aliquots with a in these 3 aliquots with a

spectrophotometer at 525 nanometers (nm).spectrophotometer at 525 nanometers (nm).

SAMPLE PREPARATIONSAMPLE PREPARATION

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

• TheThe standard addition standard addition method method is used eliminate or reduce is used eliminate or reduce interference from the sample interference from the sample matrix. It has 3 steps.matrix. It has 3 steps.

• First, the signal from a First, the signal from a sample is measured.sample is measured.

• Second, the signal from a Second, the signal from a mixture of this sample and a mixture of this sample and a known amount of standard is known amount of standard is measured.measured.

• Third, these data are used to Third, these data are used to calculate the concentration of calculate the concentration of analyte in the sample.analyte in the sample.

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• Dilute each of the 3 aliquots to 100 mL in volumetric flasks.Dilute each of the 3 aliquots to 100 mL in volumetric flasks.• What is the purpose of Aliquot 1?What is the purpose of Aliquot 1?• All the Mn is from the sample. All this Mn is oxidized to MnOAll the Mn is from the sample. All this Mn is oxidized to MnO44

––. Aliquot . Aliquot

1 is used to measure the concentration of Mn in the sample.1 is used to measure the concentration of Mn in the sample.• What is the purpose of Aliquot 2?What is the purpose of Aliquot 2?• All the Mn is from the sample and the standard. All this Mn is oxidized All the Mn is from the sample and the standard. All this Mn is oxidized

to MnOto MnO44––. Aliquot 2 is used to measure the total concentration of Mn in . Aliquot 2 is used to measure the total concentration of Mn in

the sample and in the standard.the sample and in the standard.• What is the purpose of Aliquot 3?What is the purpose of Aliquot 3?• All the Mn is from the sample. None of this Mn is oxidized to MnOAll the Mn is from the sample. None of this Mn is oxidized to MnO44

––. .

Aliquot 3 is used to set the spectrophotometer to 0 absorbance (100% Aliquot 3 is used to set the spectrophotometer to 0 absorbance (100% transmittance). This accounts for any color from the sample not from transmittance). This accounts for any color from the sample not from MnOMnO44

––. Therefore, aliquot 3 is a . Therefore, aliquot 3 is a blankblank and it is used to remove and it is used to remove

interferencesinterferences..

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• Applying Beer’s Law to this experiment:Applying Beer’s Law to this experiment:

A = abcA = abc

• A= absorbanceA= absorbance• a = the absorptivity constant for MnOa = the absorptivity constant for MnO44

––

• b = the path length of the sample cellb = the path length of the sample cell• c = the concentration of MnOc = the concentration of MnO44

–– in the sample cell in the sample cell

• Since a (absorptivity) and b (path length) are constant for a Since a (absorptivity) and b (path length) are constant for a given wavelength and a given sample cell, A (absorbance) given wavelength and a given sample cell, A (absorbance) is directly proportional to c (concentration):is directly proportional to c (concentration):

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• Furthermore, absorbances are additive:Furthermore, absorbances are additive:

AAtotaltotal = A = A11 + A + A22 + A + A33 + … + …

• The absorbance of aliquot 1 (AThe absorbance of aliquot 1 (Aaliquot1aliquot1) is caused by the Mn from the ) is caused by the Mn from the

sample being oxidized to MnOsample being oxidized to MnO44––. Therefore, the absorbance of . Therefore, the absorbance of

aliquot 1 (Aaliquot 1 (Aaliquot1aliquot1) equals the absorbance of the sample (A) equals the absorbance of the sample (Asamplesample).).

AA11 = A = Aaliquot1aliquot1 = A = Asamplesample

• The absorbance of aliquot 2 is caused by the Mn from the sample and The absorbance of aliquot 2 is caused by the Mn from the sample and standard being oxidized to MnOstandard being oxidized to MnO44

––. Therefore, the absorbance of . Therefore, the absorbance of

aliquot 2 (Aaliquot 2 (Aaliquot2aliquot2) equals the absorbance of the sample (A) equals the absorbance of the sample (Asamplesample) plus the ) plus the

absorbance of the standard (Aabsorbance of the standard (Astandardstandard).).

AA22 = A = Aaliquot2aliquot2 = A = Asamplesample + A + Astandardstandard

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• Solving for the concentration of Mn in the sample cell:Solving for the concentration of Mn in the sample cell:

• ccstandardstandard is the concentration of Mn in the sample cell. It is is the concentration of Mn in the sample cell. It is

NOT the concentration of Mn in the bottle of “Standard NOT the concentration of Mn in the bottle of “Standard Mn”.Mn”.

• ccsamplesample is the concentration of Mn in the sample cell. It is is the concentration of Mn in the sample cell. It is

NOT the concentration of Mn in steel.NOT the concentration of Mn in steel.

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, and prepared as follows.and prepared as follows.

• Afterwards, each of the 3 aliquots were diluted to 100.0 mL.Afterwards, each of the 3 aliquots were diluted to 100.0 mL. The The Standard Mn solution contained 102.6 mg of Mn / L. AStandard Mn solution contained 102.6 mg of Mn / L. Aaliquot1aliquot1 equaled equaled

0.152. A0.152. Aaliquot2aliquot2 equaled 0.376. equaled 0.376.• What is cWhat is cstandardstandard??

• Again, cAgain, cstandardstandard is the concentration of Mn in the sample cell. It is NOT is the concentration of Mn in the sample cell. It is NOT

102.6 mg of Mn / L.102.6 mg of Mn / L.

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, and prepared as follows.and prepared as follows.

• Afterwards, each of the 3 aliquots were diluted to 100.0 mL.Afterwards, each of the 3 aliquots were diluted to 100.0 mL. The The Standard Mn solution contained 102.6 mg of Mn / L. AStandard Mn solution contained 102.6 mg of Mn / L. Aaliquot1aliquot1 equaled equaled

0.152. A0.152. Aaliquot2aliquot2 equaled 0.376. equaled 0.376.

• What is cWhat is csamplesample??

• Again, cAgain, csamplesample is the concentration of Mn in the sample cell. It is NOT the is the concentration of Mn in the sample cell. It is NOT the

concentration of Mn in steel.concentration of Mn in steel.

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, and prepared as follows.and prepared as follows.

• Afterwards, each of the 3 aliquots were diluted to 100.0 mL.Afterwards, each of the 3 aliquots were diluted to 100.0 mL. The The Standard Mn solution contained 102.6 mg of Mn / L. AStandard Mn solution contained 102.6 mg of Mn / L. Aaliquot1aliquot1 equaled equaled

0.152. A0.152. Aaliquot2aliquot2 equaled 0.376. equaled 0.376.

• How many grams of Mn are in this steel sample?How many grams of Mn are in this steel sample?

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, A 0.306 g sample of steel is oxidized, dissolved, diluted to 100.0 mL, and prepared as follows.and prepared as follows.

• Afterwards, each of the 3 aliquots were diluted to 100.0 mL.Afterwards, each of the 3 aliquots were diluted to 100.0 mL. The The Standard Mn solution contained 102.6 mg of Mn / L. AStandard Mn solution contained 102.6 mg of Mn / L. Aaliquot1aliquot1 equaled equaled

0.152. A0.152. Aaliquot2aliquot2 equaled 0.376. equaled 0.376.

• What is the % Mn in this steel?What is the % Mn in this steel?

AliquotAliquot Concentrated Concentrated HH33POPO

44

Standard Standard MnMn

KIOKIO44

112233

3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL3 to 5 mL

0.00 mL0.00 mL5.00 mL5.00 mL0.00 mL0.00 mL

0.4 g0.4 g0.4 g0.4 g0.0 g0.0 g

SAMPLE ANALYSIS BY STANDARD ADDITIONSAMPLE ANALYSIS BY STANDARD ADDITION

• Give at least 1 safety concern for the following procedure.Give at least 1 safety concern for the following procedure.

• Using acids (HNOUsing acids (HNO33 and H and H33POPO44), oxidizing agents (HNO), oxidizing agents (HNO33, ,

(NH(NH44))22SS22OO88, KIO, KIO44, and KMnO, and KMnO44), and reducing agents (Mn), and reducing agents (Mn2+2+

and NaHSOand NaHSO33).).

• These are irritants. Wear your goggles at all times. These are irritants. Wear your goggles at all times. Immediately clean all spills. If you do get either of these in Immediately clean all spills. If you do get either of these in your eye, immediately flush with water.your eye, immediately flush with water.

• Your laboratory manual has an extensive list of safety Your laboratory manual has an extensive list of safety procedures. Read and understand this section.procedures. Read and understand this section.

• Ask your instructor if you ever have any questions about Ask your instructor if you ever have any questions about safety.safety.

SAFETYSAFETY

• Harris, D.C. 1999. Quantitative Chemical Analysis, 5th ed. New York, Harris, D.C. 1999. Quantitative Chemical Analysis, 5th ed. New York, NY: W.H. Freeman Company.NY: W.H. Freeman Company.

• McMurry, J., R.C. Fay. 2004. Chemistry, 4th ed. Upper Saddle River, NJ: McMurry, J., R.C. Fay. 2004. Chemistry, 4th ed. Upper Saddle River, NJ: Prentice Hall.Prentice Hall.

• Merriam-Webster, Inc. 1987. Webster’s 9th New Collegiate Dictionary. Merriam-Webster, Inc. 1987. Webster’s 9th New Collegiate Dictionary. Springfield, MA: Merriam-Webster, Inc.Springfield, MA: Merriam-Webster, Inc.

• Petrucci, R.H. 1985. General Chemistry Principles and Modern Petrucci, R.H. 1985. General Chemistry Principles and Modern Applications, 4th ed. New York, NY: Macmillan Publishing Company.Applications, 4th ed. New York, NY: Macmillan Publishing Company.

• San José State University. 2007. Photometric Determination of San José State University. 2007. Photometric Determination of Manganese in Steel. Available: Manganese in Steel. Available: http://www.sjsu.edu/faculty/chem55/55phot.htm [accessed 22 February [accessed 22 February 2007].2007].

• Specialty Steel Industry of North America. 2006. SSINA: Stainless Specialty Steel Industry of North America. 2006. SSINA: Stainless Steel: About. Available: Steel: About. Available: http://www.ssina.com/index2.html [accessed 12 [accessed 12 October 2006].October 2006].

• Tro, NJ. 2008. Chemistry, A Molecular Approach. Upper Saddle River, Tro, NJ. 2008. Chemistry, A Molecular Approach. Upper Saddle River, NJ: Prentice Hall.NJ: Prentice Hall.

SOURCESSOURCES