Titrimetry

A common laboratory method for chemical quantitative analysis

where a titrant is slowly added until an equivalence

pt is reached

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Terms

a. Analyte

b. Titrant c. Equivalence pt

d. Indicator

e. End pt

Types of Titration

a. Coulometric Titration: The Titrant is a Constant Direct Electrical Current

b. Volumetric Titration: Based on volume of Titrant is used

c. Gravimetric Titration: Based on weight of Titrant used

Coulometric Titration Au3+ + 3e Au

e (titrant)

Electrode

Volumetric Titration

Titrant in biuret (Reagent of Known Conce.g. NaOH

Analyte (unknown Conc)

e.g. Acetic Acid

CH3COOH + NaOH CH3COO- + H2O

At Equivalence pt 1 mole CH3COOH: 1 mole NaOH

Indicator: Phenoplthalein

End Point: point where color changes From colorless to pink

Primary Reference Standard: Standards that dont need to be

standardized1. High Purity

2. Atmospherically Stable

3. Non Hygroscopic

4. Reasonable High Molar Mass

5. Reasonable Solubility

6. Preferably Certified by a Recognized Organization (USP, BP and NIST)

Secondary Reference Standard :Reagents that need to be

Standardized against a primary reference standard

e.g. NaOH Solutions Standardized Using KHP

Concentration of Standard Solutions

a. Molarity ( moles per liter )

b. Normality ( moles equivalents per liter)

Equivalents: Number of Reacting Species

Depends on the Reaction Involved

For Acid/ Base Reactions: H+ and OH-

For Redox Reaction: electrons

Acid/Base Titrations (Reacting Species: H+ and OH- )

Ca(OH)2 + 2HCl CaCl2 + 2H2O

1 mole 2 mole

2 equivalents 2 equivalents

Reacting Species

OH- + H+ H20

Acid/Base Titrations (Reacting Species: H+ and OH- )

a. 1mole NaOH...1 moles equivalents

b. 1mole H2SO4...2 moles equivalents

c. 1 mole H3PO4

..3 moles equivalents

d. 2 moles Ca(OH)2

..4 moles equivalents

b. 0.5 moles Fe(OH)3

..1.5 moles equivalents

Acid/Base Titrations (Reacting Species: H+ and OH- )

Molarity = moles/L

Normality = equivalents/La. 1 molar of NaOH.....1 Normal

b. 1 molar of H2SO4....2 Normal

c. 1 molar of H3PO4...3 Normal

d. 0.25 molar of Fe(OH)3..0.75 Normal

Acid/Base Titrations (EW = grams/mole equivalent )

a. 1mole NaOH ...1 mole equivalents

(MW = 40 g )(EW = ? )

b. 1mole H2SO4...2 moles equivalents

(MW = 98g )... (EW = ? )

c. 1 mole H3PO4..3 moles equivalents

(MW = 98 g) .(EW = ? g )

Equivalent Weight (EW)

EW = MW/n

n= mole equivalents / mole compound

Acid/Base Titrations (EW = grams/mole equivalent )

a. 1mole NaOH ...1 mole equivalents

(MW = 40 g )(EW = ? )

b. 1mole H2SO4...2 moles equivalents

(MW = 98g )... (EW = ? )

c. 1 mole H3PO4..3 moles equivalents

(MW = 98 g) .(EW = ? g )

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Problem 1

How many grams of H2SO4 is needed to Prepare a 100 ml 0.2N H2SO4 solution?

MW H2SO4 = 98 grams/mole

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Problem 2

How many mole equivalents H2SO4 are in 200 ml 0.1N H2SO4 solution?

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Problem 3

Given a 200 ml 0.1N H3PO4 solution

(MW = 98 g/mole)

a. What is the molarity of the solution?b. How many equivalents of H3PO4 are there?

c. How many grams of H3PO4 are there?

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Problem 4

Normality in Redox Reactions (Based on Electrons Transferred)

MnO4- + 5Fe2+ + 8H+

Mn2+ + 5Fe3+ + 4 H2O

Determine the moles equivalents of based on the above reaction

2 moles FeCl3

.. 2 moles equivalents

2 moles KMnO4

10 moles equivalents

Determine the Normality of the Following Solutions based on the

above reaction 2M FeCl3

.. 2 N FeCl3

5M KMnO4

25 N KMnO4

Why use Normality or Molarity?

Sometimes it is more convenient because there is no need for

stoichiometry

Ratio of Mole Equivalents is always 1:1

Problem 5

10 ml of a 0.02 M (0.1N) solution of KMnO4- is needed to titrate a 2 grams sample containing FeCl2 (MW = 126.8 g).

a. What is the % mass of FeCl2 in your sample?

MnO4- + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4 H2O

Problem 6

10 ml of a 0.02 M (0.1N) solution of KMnO4 is needed to titrate a 20 ml solution of FeCl2 (MW = 126.8 g).

a. What is the molarity of FeCl2 in your sample? MnO4- + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4 H2O

TitrimetryTermsTypes of TitrationCoulometric TitrationVolumetric TitrationPrimary Reference Standard: Standards that dont need to be standardizedSecondary Reference Standard : Reagents that need to be Standardized against a primary reference standardConcentration of Standard SolutionsEquivalents: Number of Reacting SpeciesAcid/Base Titrations (Reacting Species: H+ and OH- )Slide 11Slide 12Acid/Base Titrations (EW = grams/mole equivalent )Equivalent Weight (EW)Slide 15Problem 1Problem 2Problem 3Problem 4Normality in Redox Reactions (Based on Electrons Transferred)Determine the moles equivalents of based on the above reactionDetermine the Normality of the Following Solutions based on the above reactionWhy use Normality or Molarity?Problem 5Problem 6