Final answer:
AgCl will precipitate first when a mixture of Cl- and I- is titrated with Ag+ due to its lower precipitation threshold despite having a higher Ksp than AgBr. The determination of which halide precipitates first depends on their concentration and the Ksp values.
Step-by-step explanation:
When a mixture of chloride (Cl-) and iodide (I-) ions is titrated with Ag+, AgCl will precipitate out first because it requires a lower concentration of Ag+ to begin forming the precipitate. The solubility product constant (Ksp) of AgCl is higher than that of AgBr, yet AgCl precipitates first due to the significant difference in initial ion concentrations. However, in the case where the concentrations of Cl- and I- ions are about equal, the silver halide with the smaller Ksp, which would be AgI, would precipitate first. It's important to calculate the concentration of Ag+ at which each silver halide begins to precipitate to determine which one forms first.
During the titration process, most of the time, the reaction follows this pattern:
Ag+ (aq) + Cl- (aq) → AgCl (s)
This is because AgCl starts to precipitate at lower Ag+ concentrations compared to other silver halides like AgBr or AgI. If AgNO3 solution is added to a solution containing halide ions, the identity of the halide can be determined based on the color of the precipitate formed.