Answer:
[tex][I^-]=4.6*10^{-8}M[/tex]
Explanation:
The expression of the Ksp:
[tex]Ksp_{AgCl}=[Ag^{+}][Cl^-][/tex]
[tex]Ksp_{AgI}=[Ag^{+}][I^-][/tex]
When the product of the concentrations of both ions equals the Ksp, the salt starts to precipitate.
For the AgCl:
[tex]1.8*10^{-10}M^{2}=[Ag^{+}]*0.1M[/tex]
[tex][Ag^{+}]=1.8*10^{-9}M[/tex]
Initially the concentration of I- was 0.1 M, due to the lower Ksp than the AgCl's, the AgI will precipite before. So, when AgCl starts to precipitate the concentration of I- will be in equilibrium, following the Ksp equation.
[tex]8.3*10^{-17}M^{2}=1.8*10^{-9}M*[I^-][/tex]
[tex][I^-]=4.6*10^{-8}M[/tex]
