1 Solutions Chapter 16

2 Some Definitions A solution is a homogeneous mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

3 Parts of a Solution SOLUTE – the part of a solution that is being dissolved (usually the lesser amount) SOLVENT – the part of a solution that dissolves the solute (usually the greater amount) Solute + Solvent = Solution SoluteSolventExample solid Alloys (mix of metals) Ex: brass solidliquidIonic substances (salts) in water gassolidBag of flour liquid Vinaigrette salad dressing gasliquidCarbonated drink (CO 2 dissolved) gas Air

4 IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO 4 in water K + (aq) + MnO 4 - (aq)

5 How do we know ions are present in aqueous solutions? Pure water does NOT conduct electricity! The solutions DO! They are called ELECTROLYTES HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions

6 Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugarethanol ethylene glycol Examples include: sugarethanol ethylene glycol

7 Definitions Solutions can be classified as saturated or unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature. An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

8 Definitions SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved Supersaturated solutions are unstable. The supersaturation is only temporary, and usually accomplished in one of two ways: 1.Warm the solvent so that it will dissolve more, then cool the solution 2.Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

9 Solubility Indicated how much substance (in g) can be dissolved in a given quantity of solvent at given temperature and pressure to produce a saturated solution If liquids can NOT be mixed - immisible

10 Factors affecting Solubility How fast you can dissolve Temperature (direct) Agitation/stirring (direct) Particle size (direct, because you increase surface area ) How much you can dissolve Temperature (for solids – direct, for gases – inverse) Pressure (for solids – no effect, for gases – direct)

11 Concentration of Solute The amount of solute in a solution is given by its concentration The amount of solute in a solution is given by its concentration. Molarity (M) = n (moles solute) V (liters of solution)

12 Dilution By adding water to a solution, we are diluting it, therefore lowering the initial concentration. The formula for Dilution problems: M 1 x V 1 = M 2 x V 2 initial solutiondiluted solution

13 Colligative Properties On adding a solute to a solvent, the properties of the solvent are modified. Vapor pressure decreasesVapor pressure decreases Melting point decreasesMelting point decreases Boiling point increasesBoiling point increases Osmosis is possible (osmotic pressure)Osmosis is possible (osmotic pressure) These changes are called COLLIGATIVE PROPERTIES. They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles.

14 Change in Freezing Point The freezing point of a solution is LOWER than that of the pure solvent Pure water Ethylene glycol/water solution

15 Change in Freezing Point Common Applications of Freezing Point Depression Propylene glycol Ethylene glycol – deadly to small animals

16 Common Applications of Freezing Point Depression Which would you use for the streets of Bloomington to lower the freezing point of ice and why? Would the temperature make any difference in your decision? a)sand, SiO 2 b)Rock salt, NaCl c)Ice Melt, CaCl 2 Change in Freezing Point

17 Change in Boiling Point Common Applications of Boiling Point Elevation