Question

What is the difference between Qsp and Ksp?

Answer 1

Well, `K_"sp"` is an actual equilibrium constant, that is experimentally measured..........

Explanation:

And `Q`, the so-called ion product, is a TRANSIENT, non-equilibrium value.

For a sparingly soluble salt, `MX_n`, certainly we can measure a constant for the equilibrium reaction for a given temperature:

`MX_n(s) rightleftharpoonsM^(n+) + nX^-`

And `K_"sp"=[M^(n+)][X^-]^n`

And likewise we so define `Q=[M^(n+)][X^-]^n`.

If `Q=K_"sp"`, then equilibrium has been reached, and no MACROSCOPIC change will occur. If `Q<K_"sp"`, then any precipitate will go up into solution. At `Q>K_"sp"`, then precipitation will occur.