[dagr8est]

Say you had a saturated solution of Fe(OH)₃.  Would adding solid Fe(NO₃)₃ change the solubility of the solution?

I think no because if the solution is already saturated, how can the solid dissociate into ions?  I'm not sure though.  That is why I'm asking.

[Borek]

What is solubility of the solution?

Have you heard about common ion effect?

[dagr8est]

Solubility is the amount of solid that can be dissolved in a given volume of solvent at a given temperature.  Yes, I've learned the common ion effect.

I understand that the solubility will decrease if Fe(NO₃)₃ can dissociate into ions but the solution is already saturated so how can a solid dissolve to increase the concentration of Fe⁺³?

[Borek]

Solubility is the amount of solid

So it is solubility of the solid (hydroxide in your case), not of the solution

I understand that the solubility will decrease if Fe(NO₃)₃ can dissociate into ions but the solution is already saturated so how can a solid dissolve to increase the concentration of Fe⁺³?

Apart from the volume changes it doesn't matter whether you add solid salt like Fe(NO₃)₃ or solution containing this salt. Final equilibrium will be identical.

Note that ypu will get exactly the same effect starting with Fe(NO₃)₃ solution and adding aolid Fe(OH)₃.