Ionic compounds dissolve readily in water. To separate them, different methods of precipitating the ionic compounds can be used. Ionic compounds can be precipitated by reducing the volume of the water, adding chemicals to precipitate the compounds or lowering the temperature of the water. Each of these methods can be used to separate ionic compounds. Ionic compounds can also be separated by changing the pH of the water.
Things You'll Need
- Ionic compound solution in water
- Organic solvent
- Heat source
- Chemicals to precipitate ionic compounds
- Chemicals to adjust the pH
Evaporate the water. Ionic compounds become less soluble at higher concentrations. This can be achieved by reducing the amount of water in the solution. Heat or boil the solution to remove excess water. Ionic compounds will start to crystallize and precipitate as the water evaporates and their concentration increases.
Cool the solution. Most ionic compounds become less soluble in colder solutions. A combination of evaporating the water and then cooling the water should eventually produce solid precipitates of ionic compounds.
Add an organic solvent such as an alcohol or acetone. Organic solvents make most ionic compounds less soluble. Evaporate as much water as possible to minimize the amount of organic solvent you have to add. Add solvent and stir until a precipitate forms.
Add a chemical to precipitate the ionic compound. Some ionic compounds are very soluble in water, like potassium sulphate. However, calcium sulphate is not very soluble in water. To precipitate sulphate, add a calcium salt such as calcium chloride. The calcium will pair with the sulfate and precipitate out of the solution.
Change the pH. Some ionic compounds are only soluble in a certain pH range. Add acid or base to change the pH of the solution to precipitate ionic compounds with a narrow pH range of solubility. The pH precipitation method is used for biological ionic compounds such as protein and DNA.
- Photo Credit molecules of the chemical formula image by Oleg Verbitsky from Fotolia.com
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