Lecture 22 10/26/05

Outer curve: 25 mL of M I - titrated with M Ag + Middle curve: 25 mL of M I - titrated with M Ag + Inner curve: 25 mL of M I - titrated with M Ag +

25.00 mL of M halide titrated with M Ag + Unknowns: Different anions Same volumes

40.0 mL of M KI plus 0.05 M KCl titrated with M AgNO 3

End-point detection for precipitation reactions Electrodes Silver electrode Turbidity Solution becomes cloudy due to precipitation Indicators Volhard Fajans

Volhard (used to titrate Ag + ) As an example: Cl - is the unknown Precipitate with known excess of Ag + Ag + + Cl -  AgCl(s) Isolate AgCl (s), then titrate excess Ag + with standard KSCN in the presence of Fe +3 Ag + + SCN -  AgSCN(s) When all the Ag + is gone: Fe +3 + SCN -  FeSCN 2+ (red color indicates end point) Must be acidic….WHY?

Fajans (use adsorption indicator) Anionic dyes which are attracted to positively charged particles produced after the equivalence point Adsorption of dye produces color change Fluorescein is common dye Signals end-point

Titration of strong acid/strong base 50 mL of 0.02 M KOH with 0.1 M HBr

50 mL of 0.02 M KOH with 0.1 M HBr Construct curve from 4 points Initial pH X = 0 mL, Y = ? Equivalence point X = V eq, Y = 7 Before Equivalence point X = ?, Y = ? After Equivalence point X = ?, Y = ?