Q1.
What do you think will happen if you make a saturated solution at a higher temperature and cool it slowly?
Answer
Part of the dissolved solute will come out of the solution as pure solid crystals. This is the process of crystallization.
Saturated solution of compound B at 60 °C: 287 g in 100 g of water
Solubility of B at 40 °C (from Fig. 5.6): 241 g per 100 g of water
Mass that must separate out = 287 g − 241 g = 46 g
Solubility of B at 40 °C (from Fig. 5.6): 241 g per 100 g of water
Mass that must separate out = 287 g − 241 g = 46 g
Why it happens: A saturated solution holds the maximum the solvent can carry at that temperature. When the temperature falls, that maximum falls with it, so the solution now holds more solute than it is allowed to. The extra solute has nowhere to go but out, and it leaves the solution as solid. If the cooling is slow, the particles have time to arrange themselves in a regular geometric pattern and you get large, well-shaped, shiny crystals; if it is rapid, many tiny crystals form at once and each stays small.
Did you know? Impurities usually stay dissolved because they are present in small amounts and are nowhere near their own saturation level. That is why crystallization gives a pure solid and is used to purify compounds.