Question

How would you use Le Chatelier's principle to predict whether the solubility of `BaF_2` will increase, decrease, or remain the same on addition of each of the following substances?

`HCl`
`KF`
`NaNO_3`
`Ba(NO_3)_2`

Answer 1

We examine the solubility equilibrium:

`BaF_2(s) rightleftharpoons Ba^(2+) + 2F^-`

Explanation:

Addition of `HCl` would protonate `F^-`, and drive equilibrium to the right, i.e. bring more of the fluoride into solution.

Addition of soluble `KF` increases `F^-`, and equilibrium is driven to the left.

Addition of sodium nitrate, should have no effect.

And, clearly, addition of soluble barium nitrate should drive equilibrium to the left (by increasing `[Ba^(2+)]`), and barium fluoride should precipitate.