Final answer:
The concentration of added silver ion (Ag+) needed to cause precipitation of silver halides depends on the Ksp values of AgCl and AgBr. AgCl precipitates at a lower Ag+ concentration than AgBr, so in a solution with equal Cl- and Br- concentrations, AgCl will precipitate first.
Step-by-step explanation:
The concentration of added silver ion (Ag+) required to cause precipitation of silver chloride (AgCl) and silver bromide (AgBr) can be understood by analyzing the solubility product constants (Ksp) of these compounds. Precipitation begins when the product of the concentrations of the ions in the solution exceeds this Ksp value. For example, if a solution is 0.050 M in both Cl- and Br- ions, we need to consider the Ksp values for both AgCl and AgBr to determine which will precipitate first.
Since AgCl has a higher Ksp than AgBr, it requires a lower concentration of Ag+ to begin precipitating. Therefore, adding silver nitrate (AgNO3) to the mixture would result in AgCl precipitating first since the chloride ion concentration (Cl-) in the initial mixture would typically be greater. It's essential to know that silver chloride is more soluble than silver bromide. However, due to the higher initial concentration of chloride ions in the mixture, silver chloride starts to precipitate at a lower [Ag+] concentration than silver bromide.