Lecture 2 - Lecture 2 Chapter 6: Titrimetry Normality...

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Anal Chem 251 Lect 2 1 Lecture 2 • Chapter 6: Titrimetry • Normality (Concentration of Solutions)
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Anal Chem 251 Lect 2 2 Titrimetry (Classical Method of Analysis) • Titrimetric methods or titrations are based on measuring the amount of a reagent of known concentration that reacts with the unknown (or is consumed by the unknown). • The unknown is referred to as the analyte. • Stoichiometry should be known.
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Anal Chem 251 Lect 2 3 Types of Titrimetry (or Titrations) Volumetric Titrimetry : It involves measuring the volume of a solution of known concentration that is needed to react completely with the analyte. Gravimetric Titrimetry : It involves measuring the mass of a solution of known concentration that is needed to react completely with the analyte. Coulometric Titrimetry : The “reagent” is a constant direct electrical current of known magnitude that consumes the analyte; the time required and therefore the total charge to complete the electrochemical reaction is measured.
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Anal Chem 251 Lect 2 4 Volumetric Titrations Acid-Base Titrations : Analyte and titrant undergo neutralization reactions H + + OH - H 2 O K= 1/K w = 1/10 -14 = 10 14 (We can say the reaction goes to completion) Precipitation Titrations : Based on reactions that yield ionic compounds of limited solubility. The most widely used standard solution is silver nitrate. It is used for the determination of halides. Ag + (aq) + Cl - (aq) AgCl (s) Redox Titrations : Analyte and titrant undergo electron transfer Ex/ Aqueous solutions of ~3% w/w of H 2 O 2 are sold. To measure the content, one can use a standard solution of KMnO4 5 H 2 O 2 + 2 MnO 4 - + H+ 5O 2 + 2 Mn 2+ + 8H 2 O Complexometric Titrations : Analyte and titrant involve complex formation Ex/ EDTA (ethylenediaminetetraacetic acid) can be used to titrate most metals
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Anal Chem 251 Lect 2 5 Principles and Terms of Analytical Chemistry Standard Solution (Standard Titrant) : It is a reagent of known concentration that is used to carry out the titration. •A titration is a procedure in which increments of the known reagent solution, the titrant is added to the analyte (unknown) until the reaction is complete. Titrant is usually delivered from a buret. Each increment of titrant should be completely and quickly consumed by the reaction with analyte, until the analyte is used up.
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Anal Chem 251 Lect 2 6 Figure 6-1 Typical set-up for a titration. The analyte is contained in the flask and titrant is in the buret . The stirring bar is a magnet coated with teflon, which is inert to almost all solutions. The bar is spun by rotating magnet inside the stirrer.
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Lect 2 7 Principles and Terms of Analytical Chemistry (Cont’d) •A n indicator is a compound with a physical property (usually color) that changes abruptly when the titration is complete. The change is caused by the disappearance of analyte or by the appearance of excess titrant.
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Lecture 2 - Lecture 2 Chapter 6: Titrimetry Normality...

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