1 / 12

Ch 6 Precipitation Titrations, Sec 6-5 and 6-6

Ch 6 Precipitation Titrations, Sec 6-5 and 6-6. Titration of a Mixture. e.g. A mixture of Cl - and I - is titrated with Ag + . Which halide precipitates out first? K sp AgCl = 1.8 x 10 -10 , K sp AgI = 8.3 x 10 -17. Measuring the Titration Curve in Precipitation Titrations. Fig 6-5.

adamma
Download Presentation

Ch 6 Precipitation Titrations, Sec 6-5 and 6-6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch 6 Precipitation Titrations, Sec 6-5 and 6-6

  2. Titration of a Mixture e.g. A mixture of Cl- and I- is titrated with Ag+. Which halide precipitates out first?Ksp AgCl = 1.8 x 10-10, Ksp AgI = 8.3 x 10-17

  3. Measuring the Titration Curve in Precipitation Titrations

  4. Fig 6-5

  5. Extracting Results From Figure 6-5 In curve (a) in Figure 6-5, 40.00 mL of unknown solution containing both I- and Cl- were titrated with 0.0845 M Ag+. Calculate the Molarity of each ion.

  6. There are three common types of precipitation titrations - • Mohr Method - CrO42- indicator(yellow to red) • Volhard Method - back titration of excess Ag+ with SCN-, Fe3+ indicator(clear to red) • Fajans Method - adsorption indicator = dichlorofluorescein anion (pink at endpoint)

  7. Mohr Method Titration of a halide (Cl-, Br-, I-) with AgNO3 to form a precipitate using K2CrO4 as the indicator. e.g. Ag+ + Cl-→ AgCl eq. pt. color change to red The indicator combines with excess Ag+ at the eq. pt. Before the eq. pt., the solubility of the Ag-halide precipitate must be less than the Ag-indicator, otherwise the latter would precipitate out during the titration! 2 Ag+ + CrO42- → Ag2CrO4(s) red Ag+ + Cl- → AgCl(s) white

  8. Volhard Method • Excess AgNO3 is added to precipitate out all of the halide. • The excess Ag+ is back-titrated with KSCN using Fe3+ as the indicator • e.g. Ag+ + Cl-→ AgCl(s) • added in excess • then Ag+ + SCN-→ AgSCN(s) • excess titrant • after the endpoint - • Fe3+ + SCN- → FeSCN2+ • [Cl-] = total Ag+ - amount backtitrated

  9. Fajans Method The indicator adsorbs onto the colloid particles after the eq. pt. and changes color to pink. Adsorption Indicator - Dichlorofluorescein

  10. before the eq. pt. the lattice ion in excess is the halide (Cl- etc) so the colloid is negatively charged after the eq. pt. the lattice ion in excess is the titrant Ag+ so the colloid is positively charged and then the negative adsorption indicator will bind and change color.

More Related