why doesn't solute added to a saturated solution dissolve
When a solution is saturated, it means that the maximum amount of solute has already dissolved in the solvent at a given temperature. In this state, the solution is in equilibrium, with the rate of dissolution being equal to the rate of precipitation of the solute.
If more solute is added to a saturated solution, it will not dissolve because there is already an excess of solute particles in the solution. The additional solute particles will not be able to fit into the solvent and will remain as undissolved solid particles.
To understand why this happens, we can think of solubility as a limit to the amount of solute that can be dissolved in a given amount of solvent. If this limit is reached, the solution is saturated, and any further addition of solute will not be soluble.
One way to visualize this is to imagine a glass of water as the solvent and sugar as the solute. Initially, you can keep adding sugar to the water and it will dissolve. However, once the water becomes saturated with sugar, adding more sugar will not make it dissolve. Instead, the excess sugar will settle at the bottom of the glass.
In summary, when a solution is saturated, it means that the solute has reached its maximum solubility in the solvent. Any additional solute added will not be able to dissolve because the solution is already at equilibrium.