#Solubility Equilibria and the Common Ion Effect

Hey there, future AP Chem master! Let's dive into how solubility changes when we're not just dealing with pure water. It's all about the common ion effect, and it's a game-changer! 💡

This topic is crucial because it connects solubility, equilibrium, and Le Chatelier's principle—all big hitters on the AP exam. Expect to see it in both multiple-choice and free-response questions.

#The Common Ion Effect: What is it?

The common ion effect is a fancy way of saying that if you add a salt that shares an ion with another salt already in solution, the solubility of the second salt goes down. It's like adding more of one ingredient to a recipe – it throws off the balance. Think of it as a crowded dance floor; if there are already a lot of dancers of one type, it's harder for more of that type to join in!

#Key Points

• A common ion is an ion that is present in two or more different compounds.
• Adding a common ion to a solution decreases the solubility of a slightly soluble salt.
• This effect is a direct result of Le Chatelier's Principle.

#How Does it Work? 🤔

Let's say we have a salt, $AB$, that dissolves like this:

$$AB(s) \rightleftharpoons A^+(aq) + B^-(aq)$$

The solubility product, $K_{sp}$, is:

$$K_{sp} = [A^+][B^-]$$

Now, if we add a salt like $NaB$, which also has $B^-$ ions, we're increasing the concentration of $B^-$ in the solution. According to Le Chatelier's Principle, the equilibrium will shift to the left, favoring the formation of the solid $AB$ and reducing the solubility of $AB...