Solutions are one of the most important topics in all of chemistry. Most chemical reactions take place in aqueous solutions, including biochemical reactions in our blood. Because the amount of stuff dissolved in a liquid has a huge effect on how that liquid behaves, we need to know how to define concentration. A homogeneous mixture of one or more substances dissolved in another substance.

Examples of Solutions Alloys – Air – a solution of gases Aqueous solutions – things dissolved in water Ex) salt water, Kool-Aid Ex) salt water, Kool-Aid solutions of metals Ex) Brass = zinc + copper

Properties of Liquid Solutions Solutions are homogeneous mixtures Solutions are transparent and do not disperse light Solutions can have color Solutions will not settle on standing Solutions will pass through a filter SolutionColloid

Parts of a Solution Solute = The substance being dissolved – present in the smaller amount Solvent =The substance that dissolves the solute – present in the larger amount

Label the Parts: SolutionSolventSolute Chocolate Milk: Choc. Syrup + Milk Kool-Aid: Water + Drink Powder Seltzer: CO 2 + Water Milk Choc. Syrup Water Drink Powder Water CO 2

Concentrations Unsaturated - Saturated - Can still dissolve more solute. If you place sugar in your iced tea you’ve made an unsaturated solution, because if you were to add more sugar, it would also dissolve. Has dissolved as much solute as it possibly can. If you added sugar to your iced tea until it was saturated, any sugar you add after that point sinks to the bottom, never dissolving.

Concentrations Cont. Supersaturated - Holds more solute than a saturated solution at the same temperature - Very unstable. If you added sugar to your iced tea when it was supersaturated, all of the dissolved sugar would suddenly crystallize out.

Solubility Factors Can anything dissolve? What factors can affect solubility? Temperature: As T ↑ most solids become more soluble in water, but gases become less soluble Temperature: As T ↑ most solids become more soluble in water, but gases become less soluble Pressure: Doesn’t affect solids or liquids, but gases become more soluble in liquids as P ↑ Pressure: Doesn’t affect solids or liquids, but gases become more soluble in liquids as P ↑ Nature of Solute and Solvent:  Nature of Solute and Solvent: 

Nature of Solute and Solvent How does a solute dissolve? In a solution, why do substances dissolve in one another? Some of the attractive forces between the particles of each component must be overcome The particles of all of the components must be able to attract each other with forces of similar strength.

“Like Dissolves Like” If the solvent and solute are of the same polarity, dissolution will occur Let’s review polarity... Remember – polar molecules have positive and negative ends: dipoles

Polarity Review Polarity of bonds vs. polarity of molecules Polar bonds have an electronegativity difference of greater than Polar bonds have an electronegativity difference of greater than Polar molecules are asymmetrical. Polar molecules are asymmetrical. Must contain at least 1 polar bond Bond polarities do not cancel each other out “Tug of War” “Tug of War” 0.4

Polarity Practice FormulaLewis DiagramPolar? CO 2 CH 3 Cl H2OH2O (Remember that molecules have 3-D shapes!) C O O O H H C H H HCl No Yes

Polar Solutes & Solvents Salt Water Cl Na When a positive charge from a polar solvent lines up with a negative charge from a polar solute, they attract one another and the solute is pulled into solution. Dipole-Dipole Interactions

Polar Solutes A nonpolar solvent can’t get in between the polar solute ions A polar solvent can get in between the polar solute ions

Nonpolar Solutes Polar solvent molecules don’t grab on to nonpolar solutes because they’d rather be grabbing other polar solvent molecules. Nonpolar solvents dissolve nonpolar solutes because attractions between the molecules in both the solvent and the solute aren’t very strong.

Soluble or Not? Label each substance as polar or nonpolar, then decide whether the solute would dissolve or not for each given set of solutes and solvents: SolventSoluteSolution? CH 4 HCl LiBr CCl 4 I2I2 KCl Nonpolar Polar Nonpolar Polar Yes No Yes