Question

AgNO₃ is slowly added to a solution containing 0.010 M Na_₄ and 0.050 M KBr. Given: Ksp(Ag_CrO₄) = 1.1 × 10-¹²; Ksp(AgBr) = 5.0 × 10−¹³.

Show all your calculations and reasoning to prove that AgBr will precipitate first. [6]
a. AgBr has a higher Ksp value than Ag2CrO₄
b. Ag₂CrO₄ has a higher Ksp value than AgBr
c. AgBr has a lower Ksp value than Ag₂CrO₄
d. Ag₂CrO₄ has a lower Ksp value than AgBr

Answer 1

AgBr will precipitate first because it has a smaller Ksp value.

Step-by-step explanation:

If the solution contained about equal concentrations of Cl¯ and Br¯, then the silver salt with the smaller Ksp (AgBr) would precipitate first. The concentrations are not equal, however, so the [Ag+] at which AgCl begins to precipitate and the [Ag+] at which AgBr begins to precipitate must be calculated. The salt that forms at the lower [Ag+] precipitates first.