Unit 5: Solutions and Solubility Chemistry 30 Unit 5: Solutions and Solubility

Components of a Solution A solution is composed of two or more pure substances mixed together, one of which is a solvent and the other a solute. A cup of instant coffee is the solution, the hot water is the solvent, and the instant coffee is the solute. A saturated solution is a solution that contains the maximum amount of solute dissolved in a solvent. A supersaturated solution is a solution where conditions have been changed to allow more solute to dissolve than would at room temperature (this is done by heating the solvent or solution).

Components of a Solution Factors that may affect solubility are temperature and pressure: Temperature: Gases: Temp ⬆, solubility ⬇ Solids and liquids: Temp ⬆, solubility ⬆ Pressure: Gases: Pressure ⬆, solubility ⬆ Solids and liquids: unaffected

Components of a Solution Like dissolves like. That is polar covalent molecules usually dissolve in other polar covalent molecules and non-polar covalent molecules dissolve in non-polar covalent molecules.

Components of a Solution RECALL: Polarity can be determined by subtracting electronegativities. A polar molecule is one where one (or more) atom in the molecule has a stronger pull on the electrons than another atom, so the electrons move closer to the atom with the stronger pull (higher electronegativity). This creates a dipole, where the atom with the stronger pull has a slightly negative charge and the atom with the lower electronegativity (less pull) has a slightly positive charge.

Water as a Solvent: Solutions in which water is the solvent are called aqueous solutions. Most covalent liquids are only able to dissolve other covalent compounds; water can dissolve both ionic and covalent compounds. The attraction of water dipoles for ions pulls ions out of a crystalline lattice and into aqueous solution.

Aqueous Solutions: Sometimes when we mix two dissolved salts together, we end up with a precipitate. This is because a new ionic compound is formed that is insoluble in water.   We can use solubility charts or solubility tables to determine if a solid will be formed.

Ion Solubility Exceptions NO3– soluble none ClO4– Cl–  except Ag+, Hg22+, *Pb2+ I– except Ag+, Hg22+, *Pb2+ Br- SO42- except Ca2+, Ba2+, Sr2+, Hg2+, Pb2+, Ag+ CO32- insoluble except Group IA and NH4+ PO43- OH– except Group IA, *Ca2+, Ba2+, Sr2+ S2- except Group IA, IIA and NH4+ Na+ K+ NH4+

Ex. If we mix sodium ions with hydroxide ions will a precipitate form? Solubility Exceptions NO3– soluble none ClO4– Cl–  except Ag+, Hg22+, *Pb2+ I– except Ag+, Hg22+, *Pb2+ Br- SO42- except Ca2+, Ba2+, Sr2+, Hg2+, Pb2+, Ag+ CO32- insoluble except Group IA and NH4+ PO43- OH– except Group IA, *Ca2+, Ba2+, Sr2+ S2- except Group IA, IIA and NH4+ Na+ K+ NH4+  Ex. If we mix sodium ions with hydroxide ions will a precipitate form?     Ex. If we dissolved sodium hydroxide in calcium chloride, will a precipitate form? Ex. Will a mixture of calcium nitrate with sodium carbonate create a precipitate?

See Components of Solutions Assign