Dr. S. M. Condren Principles of Volumetric Analysis titration titrant analyte indicator equivalence point vs. end point titration error blank titration

Dr. S. M. Condren Principles of Volumetric Analysis primary standard 1. High purity100.02% 2. Stability toward air 3. Absence of hydrate water 4. Available at moderate cost 5. Soluble

Dr. S. M. Condren Principles of Volumetric Analysis standardization standard solution Methods for establishing concentration direct method standardization secondary standard solution

Dr. S. M. Condren Volumetric Procedures and Calculations relate the moles of titrant to the moles of analyte # moles titrant = # moles analyte #moles titrant =(V*M) titrant = #moles analyte =(V*M) analyte

Dr. S. M. Condren EXAMPLE: What is the molarity of an HCl solution if it took mL of the 0,09782 M NaOH solution to titrate mL HCl solution?

Dr. S. M. Condren EXAMPLE: What is the molarity of an HCl solution if it took mL of the above NaOH solution to titrate mL HCl solution? at equivalence point: # moles acid = # moles bases V acid x M acid = V base x M base

Dr. S. M. Condren EXAMPLE: What is the molarity of an HCl solution if it took mL of the above NaOH solution to titrate mL HCl solution? at equivalence point: # mL acid x M acid = # mL base x M base # mL base x M base M acid = # mL acid

Dr. S. M. Condren EXAMPLE: What is the molarity of an HCl solution if it took mL of the above NaOH solution to titrate mL HCl solution? at equivalence point: # mL base X M base M acid = # mL acid (39.72 mL)( M) = = M (25.00 mL)

Dr. S. M. Condren Acid-Base Indicators

Dr. S. M. Condren Figure 7.5 Spectrophotometric Titration

Dr. S. M. Condren Precipitation Titration Curve p-functionpX = - log 10 [X] precipitation titration curve four types of calculations initial point before equivalence point equivalence point after equivalence point

Dr. S. M. Condren Precipitation Titration Curve EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. titration curve => pAg vs. vol. AgNO 3 added

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. titration curve => pAg vs. vol. AgNO 3 added initial point after 0.0 mL of AgNO 3 added at the initial point of a titration of any type, only analyte is present, no titrant is present, therefore pAg can not be calculated.

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point pAg can be accurately calculated only after some AgBr has started to form. This may take a few mL of titrant

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added V NaBr *M NaBr - V AgNO3 *M AgNO3 M NaBr unreacted = V NaBr + V AgNO3

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added V NaBr *M NaBr - V AgNO3 *M AgNO3 M NaBr unreacted = V NaBr + V AgNO3 (50.00mL* M) -(5.00mL* M) M NaBr unreacted = ( )mL

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added (50.00mL* M) -(5.00mL* M) M NaBr unreacted = ( )mL M NaBr unreacted = 3.64 X M

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added M NaBr unreacted = 3.64 X M [Br - ] total = [Br - ] NaBr unreacted + [Br - ] dissolved AgBr

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added M NaBr unreacted = 3.64 X M [Br - ] total = [Br - ] NaBr unreacted + [Br - ] dissolved AgBr [Br - ] total = 3.64 X M + [Ag + ] dissolved AgBr where[Br - ] dissolved AgBr = [Ag + ] dissolved AgBr

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added [Br - ] total = 3.64 X M + [Ag + ] dissolved AgBr where[Br - ] dissolved AgBr = [Ag + ] dissolved AgBr except very near the equivalence point, 3.64 X M >> [Ag + ] dissolved AgBr

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added [Br - ] total = 3.64 X M + [Ag + ] dissolved AgBr except very near the equivalence point, 3.64 X M >> [Ag + ] dissolved AgBr thus[Br - ] total ~ 3.64 X M

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added [Br - ] total ~ 3.64 X M pBr = - log 10 (3.64 X ) = 2.44

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added K sp = [Ag + ][Br - ] = 5.2 X M 2 - log K sp = - log[Ag + ] - log[Br - ] = - log(5.2 X ) pK sp = pAg + pBr = 12.28

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. before equivalence point after 5.0 mL of AgNO 3 added K sp = [Ag + ][Br - ] = 5.2 X M 2 - log K sp = - log[Ag + ] - log[Br - ] = - log(5.2 X ) pK sp = pAg + pBr = if pBr = 2.44 pAg = pK sp - pBr = = 9.84

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. equivalence point at mL of AgNO 3 added At the equivalence point, [Ag + ] = [Br - ] thus K sp = [Ag + ][Br - ] = 5.2 X M 2

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. equivalence point at mL of AgNO 3 added becomes when [Ag + ] = [Br - ] [Ag + ] 2 = 5.2 X M 2 [Ag + ] = 7.21 X M pAg = 6.14

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point After the equivalence point there is very little change in the amount of precipitate present (except very close to the equivalence point)

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point thus, at mL of AgNO 3 added V AgNO3 *M AgNO3 - V NaBr *M NaBr M AgNO3 unreacted = V AgNO3 + V NaBr

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point thus, at mL of AgNO 3 added V AgNO3 *M AgNO3 - V NaBr *M NaBr M AgNO3 unreacted = V AgNO3 + V NaBr (25.10 mL * M) - (50.00 mL * M) M AgNO3 = unreacted ( )mL

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point thus, at mL of AgNO 3 added (25.10 mL * M) - (50.00 mL * M) M AgNO3 = unreacted ( )mL M AgNO3 unreacted = 1.33 X M

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point thus, at mL of AgNO 3 added M AgNO3 unreacted = 1.33 X M [Ag + ] total = [Ag + ] AgNO3 unreacted + [Ag + ] dissolved AgBr

Dr. S. M. Condren EXAMPLE: Derive a curve for the titration of mL of M NaBr with M AgNO 3. after equivalence point thus, at mL of AgNO 3 added [Ag + ] total = [Ag + ] AgNO3 unreacted + [Ag + ] dissolved AgBr [Ag + ] total = 1.33 X M + [Ag + ] dissolved AgBr [Ag + ] total ~ 1.33 X M pAg =

Dr. S. M. Condren

Figure 7.6 Precipitation titration Curves

Dr. S. M. Condren End-Point Detection argentometric titrations 1. Mohr - titration of Cl - with AgNO 3 - K 2 CrO 4 gives brick red color to precipitate, Ag 2 CrO 4

Dr. S. M. Condren End-Point Detection argentometric titrations 2. Volhard -titration of Ag + with Cl - - KSCN in the presence of Fe +3 gives blood red color to precipitate, FeSCN +2

Dr. S. M. Condren End-Point Detection argentometric titrations 3. Fajans - titration of Cl - with AgNO 3 - absorption indicator, dye absorbs on to the surface of the particles of AgCl, attracted by excess Cl - absorbed on the surface of the precipitate

Dr. S. M. Condren