How can a saturated solution decrease in solubility?

On the Snaprevise website, it is explained that in the crystallisation process, 'cooling the saturated solution leads to a decrease in solubility, meaning more crystals are formed from the solution.'

This confuses me, because if a solution is saturated, then no more solute can be dissolved in it. I am confused what the website means by the saturated solution becoming more insoluble.

Reply 1

username3707756

Solubility changes with temperature. On cooling, there is a decrease in solubility, so less solute is dissolved in solution. The solute precipitates out

Reply 2

EierVonSatan

It's the solute that becomes less soluble.

Reply 3

luckypie

Original post by EierVonSatan

It's the solute that becomes less soluble.

I'm confused as to how that works? Because isn't the solute not soluble anymore due to the solution being saturated anyway?

Reply 4

EierVonSatan

Original post by luckypie

I'm confused as to how that works? Because isn't the solute not soluble anymore due to the solution being saturated anyway?

Solubility is how much solute can be dissolved in a given mass of solvent.

If you try to add more solute to a saturated solution of that solute, it won't dissolve. That dosen't mean that the solute is insoluble :no:

just that it can't dissolve any more into that solution.

Does this make sense?

Reply 5

username3707756

Original post by luckypie

I'm confused as to how that works? Because isn't the solute not soluble anymore due to the solution being saturated anyway?

"The solute is not soluble anymore" - this is not true. The saturated solution contains the maximum amount of solute that can dissolve in it at that temperature. It still has solute. But at the higher temperature, the solution carried more solute. When cooled, the solubility of the solute in the solvent fell, so less solute was in the solution. The solute which crashed out of solution is seen as crystals.

Solubility of a solute in a particular solvent is defined as the mass of the solute dissolved per unit mass of that solvent. The solubility varies with temperature. A saturated solution is one which contains the maximum amount of solute. e.g If I have 100g of water and a substance X has a solubility of 4g/100g water, then I can only dissolve 4g of X in it and no more. The solution then formed is called a saturated solution.