Lecture 2210/26/05

Outer curve: 25 mL of 0.100 M I- titrated with 0.0500 M Ag+

Middle curve: 25 mL of 0.0100 M I- titrated with 0.00500 M Ag+

Inner curve: 25 mL of 0.00100 M I- titrated with 0.000500 M Ag+

25.00 mL of 0.100 M halide titrated with 0.0500 M Ag+

Unknowns:

Different anions

Same volumes

40.0 mL of 0.052 M KI plus 0.05 M KCl titrated with 0.084 M AgNO3

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- FeSCN2+

• (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 = Veq, Y = 7

• Before Equivalence point• X = ?, Y = ?

• After Equivalence point• X = ?, Y = ?