To remove the crystals, you use vacuum filtration. This removes the crystals from the solution. The last step is to wash the crystals with a cold solvent, which will remove any impurities coating the surface of the crystals. You now have a purified solid. (b) (2 pts.) How do you make a “supersaturated” solution? How is this different than a “saturated” solution? Answer: To make a “supersaturated” solution, you first increase the solubility of the solution by increasing it's temperature (100 deg C if it's a water base), then add more solute. Once fully dissolved, you let the solution cool, and the excess solute will crystallize in a pure form as the solubility decreases with the temperature. (c) Describe what happens when solute is added to:[i] (1 pts.) a saturated solution Answer: The solute will not dissolve in a saturated solution because it is already at it's maximum solubility. [ii] (1 pts.) an unsaturated solution Answer: The solute will dissolve into the solution. [iii] (1 pts.) a supersaturated solution Answer: There are two possible answers to this one. If you add solute when the temperature is increased, the solubility is increased as well, so as long as It hasn't reached the expanded solubility it will dissolve. If, however, you are referring to adding it to a cooling solution that has already been turned into a supersaturated solution, the solute will not dissolve, and will sit in the solution along with the recrystallized pure form of the solute.
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- Summer '11
- Solubility, Potassium nitrate, saturation