Titration curves precipitation

By now you should understand the chemistry that occurs at different stages of a precipitation titration, and you should know how to calculate the shape of a titration curve. We now introduce spreadsheet calculations that are more powerful than hand calculations and less prone to error. If a spreadsheet is not available, you can skip this section with no loss in continuity. Consider the addition of liters of cation M+ (whose initial concentration is C ) to liters of solution containing anion X- with a concentration C%. 

The total moles of added M (= C1 VM) must equal the moles of MJ in solution (= [MxJ(Vm + V ) plus the moles of precipitated MX(i). (This equality is called a mass balance, even though it is really a mole balance). In a similar manner, we can write a mass balance for X. 

Now equate mol MX(.v) from Equation 7-16 with mol MX(.v) from Equation 7-17  

Volhard titration formation of a soluble, colored complex at the end point 

Fajans titration adsorption of a colored indicator on the precipitate at the end point 

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Sketching the Titration Curve As we have done for acid-base, complexometric titrations, and redox titrations, we now show how to quickly sketch a precipitation titration curve using a minimum number of calculations. 

How to sketch a precipitation titration curve see text for explanation. 

Fig. 25.7 Precipitation titration curve. Initial and final slopes are drawn (see Fig. 22.3) and a parallel line is drawn such that the mid-point is on the curve. This is the equivalence point.

Figure 1 3-5 Effect of reaction completeness on precipitation titration curves. For each curve, 50.00 mL of a 0.0500 M solution of the anion was titrated with 0.1000 M AgN03. Note that smaller values of ATjp give much sharper breaks at the end point.

Effect of complexation on solubihty (key equations 11.10, 11.11), p. 345 Calculating precipitation titration curves, p. 346 Indicators for precipitation titrations, p. 349... 

As with the other reaction types, the precipitation titration curve can be described by a single equation. If of a chloride solution is titrated with C gM AgN03, then at any point after the addition of mL, balance equations can be written for [Cl ] and [Ag ]. The total Ag content is distributed between dissolved Ag and precipitated AgCl. Similarly, total Cl is the sum of dissolved Cl" and precipitate. 

Using Equation 11-3, develop a series of simulated precipitation titration curves in which Ag is used to titrate three singly charged anions, X", Y", and Z, whose log K p values are -12, -9, and -6. Repeat the exercise with other sets of log K p values. How does the log K p interval affect... 

Theoretical Study of Some Precipitation Titration Curves. 679... 

FIGURE 3 Precipitation titration curves for 25 ml of 0.1 M solutions of various anions with 0.1 M AgNOs solution. 

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