Chapter 18, Problem 88FP

In the Mohr titration, ${\text{Cl}}^{-}\left(\text{aq}\right)$ is titrated with ${\text{AgNO}}_{\text{3}}$ in solutions that are pH=7. Thus it is suitable for determining the chloride ion content of drinking water. The indicator used in the titration is ${\text{K}}_{\text{2}}{\text{CrO}}_{\text{4}}\left(\text{aq}\right)$ . A red-brown precipitate of ${\text{Ag}}_2{\text{Cr}}_4\left(\text{s}\right)$ forms after all the ${\text{CI}}^{-}$ has precipitated. The titration is ${\text{Ag}}^{\text{+}}\left(\text{aq}\right)+{\text{CI}}^{\text{-}}\left(\text{aq}\right)\to \text{AgCl}\left(\text{s}\right)$ . At the equivalence point of the titration, the titeation mixture consists of AgCl(s) and a solution having neither $A{g}^{+}$ nor ${\text{Cl}}^{\text{+}}$ in excess. Also, no ${\text{Ag}}_{\text{2}}{\text{CrO}}_{\text{4}}$ is present, but it forms immediately after the equivalence point.

1. How many milliters of 0.0100M ${\text{AgNO}}_{\text{3}}\left(\text{aq}\right)$ are required to titrate 100.0 mL of a municipal water sample having 29.5 mg ${\text{Cl}}^{-}/L$?
2. What is $\left[A{g}^{+}\right]$at the equivalence point of the Mohr titration?
3. What is $\left[{\text{CrSO}}_{\text{4}}\right]$ in the titration mixture to meet the requirement of no precipition of ${\text{Ag}}_{\text{2}}{\text{CrO}}_{\text{4}}\left(\text{s}\right)$until immediately after the equivalence point?
4. Describe the effect on the results of the titration if $\left[{\text{CrO}}_{\text{4}}^{\text{2-}}\right]$were (1) greater than that calculated in part (c) or (2) less than that calculated?
5. Do you think the Mohr titration would word if the reactants were exchanged-that is, with ${\text{CI}}^{-}\left(\text{aq}\right)$as the sample being analyzed? Explain.