Presentation on theme: "Mixtures and dissolving"— Presentation transcript:
1 Mixtures and dissolving General Chemistry Unit 10
2 Types of MixturesSolution: homogeneous mixture of two or more substances in a single phaseTwo parts: solvent (greater amt) and soluteDoes not separate on standingCannot be separated by filtrationMany types of solutions (p. 81)
3 Types of mixuresSuspension: heterogeneous mixture that must be stirred to keep mixedParticles settle outParticles over 1000 nmCan be separated by filtrationNot transparent
4 Types of mixturesColloid: heterogeneous mixture with particles of intermediate sizeTwo parts: continuous and dispersed phasesParticles do not settle outParticles between nmCan be separated by a semipermeable membrane but not normal filtration
5 Classes of colloids Sol: solid in liquid (paint, mud) Gel: solid network in liquid (gelatin, pearls, opals)Emulsion: liquid in liquid or solid (milk, mayonnaise, cheese)Foam: gas in liquid or solid (whipped cream, marshmallow)Aerosol: liquid or solid in gas (fog, smoke, cloud, anything in spray can)
6 Tyndall effect Scattering of light by colloid particles Colloids/Sunset Demo (Journal)
7 The Solution Process Factors Affecting Rate of Dissolving: Crushing or breaking up: increases the surface area exposed to the solventStirring or agitating the solution: brings fresh solvent into contact with the solute particlesHeating: faster motion gives more collisions with more energy which helps separate particles from each other and disperse them in the solvent
8 SolubilityThere is a limit to how much solute can be dissolved in a certain amount of solvent.This limit is expressed as solubility (g/100 ml solvent).Solution equilibrium occurs when the rates of dissolving and crystallization are equal
9 Solution conditionsSaturated solution: contains the maximum amount of dissolved solute.Unsaturated solution: contains less than the maximum amount of dissolved solute.Supersaturated solution: contains more solute than a saturated solution under the same conditions. (Created from a saturated solution at a higher temperature that cools without forming crystals.)
10 Solution testA solution at room temperature has no crystals in it. How can we know if it is saturated, unsaturated, or supersaturated?TEST: Add more solute and observe the results.Crystal dissolves: unsaturatedCrystal drops to bottom and remains unchanged: saturatedCrystal drops to bottom and grows substantially: supersaturated
11 Dissolving ionic compounds in water Dissolving in WaterHydration occurs between water and ionic solutes.The water molecules are attracted to the ions and draw them away from the surface of the crystal.The ions are surrounded by water molecules.New ions are exposed and the process repeats, resulting in the dissolving of the entire crystal.
12 Solute-solvent interactions Like Dissolves LikePolar solvents dissolve polar (or ionic) solutes.Nonpolar solvents dissolve nonpolar solutes.Liquid solutes and solvents that are not soluble in each other are immiscible.Liquids that dissolve in each other are miscible.
13 Dissolving effects Pressure Only affects gas solubility Henry’s Law: the solubility of a gas is directly proportional to the partial pressure of the gas on the liquid’s surface.Examples of Henry’s Law:Carbonated beverages (bottled under pressure)The “Bends” experienced by divers (more gases dissolve in blood, when rising come out as bubbles and go to brain)
14 Dissolving effects Heats of Solution Energy change (heat absorbed or released) when dissolving takes placeSolid in liquid:Usually endothermic, positive value, requires energySometimes exothermic, negative value, gives off energyMost become more soluble if temperature is raisedGas in liquid:ExothermicBecomes more soluble at lower temperatures – fish die inwarm water (not enough oxygen)