Solution Solutions are homogeneous mixtures of two or more puresubstances. In a solution, the solute is dispersed uniformly throughout thesolvent. A homogenous mixture of a solute dissolved in a solvent. The solubility (ability to dissolve) of a solute in a solvent isdependent on thea. Temperature For solid solutesas temperature increases, solubility increases. For gas solutes :as temperature increases, solubility decreases.
b. Pressure For solid solutesas pressure increases, solubility remains the same. For gas solutes:as pressure increases, solubility increasesc. Nature of Solute/Solvent “Like dissolves in like.”Solute Type Non Polar Solvent Polar SolventNon Polar (Fat Grease) Soluble (Soap) Insoluble (Water)Polar Insoluble Soluble (Water)Ionic (Salt) Insoluble Soluble (Water)High Solubility-Soluble Low Solubility-insoluble
Solubility Maximum grams of solute that will dissolve in 100 g of solvent ata given temperature.Solubility= Varies with temperature Based on a saturated solutionGram of solute100 g of Water The bond between solubility andtemperature can be expressed by asolubility curve. The solubility curvesof several compounds are shown onthe right. Such curves disclose themaximum amount of solute that canbe dissolved in 100 grams of waterover a range of temperatures. The solubility of most compoundsincreases as temperature increases,although exceptions do exist.
Types of Solution1. An unsaturated solution is a solution in which more solute canbe dissolved at a given temperature.2. A saturated solution is a solution containing the maximumamount of solute that will dissolve at a given temperature.3. A supersaturated solution is a solution that contains more solutethan would dissolve in a saturated solution at a giventemperature.SATURATED SOLUTIONno more solute dissolvesUNSATURATED SOLUTIONmore solute dissolvesSUPERSATURATED SOLUTIONbecomes unstable, crystals formincreasing concentration
Saturated Solvent holds as much solute as is possible at thattemperature. Dissolved solute is in dynamic equilibrium withsolid solute particles.Types of Solution Unsaturated Less than the maximum amount of solute for that temperature isdissolved in the solvent.Saturated Supersaturated Solvent holds more solute than is normally possible at thattemperature. These solutions are unstable; crystallization can usually be stimulatedby adding a “seed crystal” or scratching the side of the flask.
Solubility Rules1. Not all ionic compounds are water soluble.2. There are some general rules for compounds that are watersoluble: Group 1 ionic compounds and ammonium (NH4+) are alwayswater soluble Group 17 ionic compounds are water soluble except when pairedwith Ag, Pb, and Hg ions1. A salt is soluble in water if it contains any one of the followingions:NH4+ Li+ Na+ K+ or NO3-Examples: Soluble saltsLiCl Na2SO4 KBr Ca(NO3)2
Solubility Rules2. Salts with Cl- are soluble, but not if the positive ion is :Ag+, Pb2+, or Hg22+.Examples:Soluble InsolubleMgCl2 AgCl , PbCl23. Salts with SO42- are soluble, but not if the positive ion is Ba2+,Pb2+, Hg2+ or Ca2+.Examples:Soluble Not solubleMgSO4 BaSO4 PbSO4
The stronger the attraction between solute and solventmolecules, the greater the solubility. Like dissolves like (the substances have similarintermolecular attractive forces.) Polar substances tend to dissolve in polar solvents. Non-polarsubstances do not dissolve in polar solvents.Factors Affecting Solubility
Chemists use the axiom “like dissolves like”: Polar substances tend to dissolve in polar solvents. Nonpolar substances tend to dissolve in nonpolar solvents.Factors Affecting Solubility The moresimilar theintermolecularattractions, themore likely onesubstance is to besoluble in another.
Glucose (whichhas hydrogenbonding) is verysoluble inwater, whilecyclohexane(which only hasdispersionforces) is not.Factors Affecting Solubility
Vitamin A is soluble in nonpolar compounds (like fats). Vitamin C is soluble in water.Factors Affecting Solubility
Concentration Concentration of a solution can be expressed either quantitativelyor qualitatively (dilute or concentrated).Methods of Expressing Concentrations of SolutionsMass Percentage Mass percentage is expressed using the equation:Mass % of component = XMass of component in solutionTotal mass of solution 100Parts per Million (ppm)ppm =mass of A in solutiontotal mass of solution106Parts per Billion (ppb)ppb =mass of A in solutiontotal mass of solution109
Mole Fraction This is how many moles of substance are in the solution.Mole fraction of component =Moles of componentTotal moles of all componentsMolarity Relates the volume of solution to the quantity of solute that itcontains.Molarity =Moles soluteLiters solutionMolality(m)mol of solutekg of solventm =Because both moles and mass do not change with temperature,molality (unlike molarity) is not temperature dependent.
Changing Molarity to MolalityIf we know the density of thesolution, we can calculate themolality from the molarity,and vice versa.
Raoult’s LawPsoln = Vapor pressure of the solutionsolvent = Mole fraction of the solventP solvent = Vapor pressure of the pure solventThe presence of a nonvolatile solute lowers the vapor pressureof a solvent.Psoln = solventP solventThe presence of anonvolatile solutelowers theconcentration of solventmolecules in thesolution, thus loweringthe vapor pressure.Demonstration of Raoult’s Law
Water is transported to thesolution due to difference invapor pressure.An Aqueous Solution and PureWater in a Closed EnvironmentDemonstration of Raoult’s Law
Psoln = solventP solventVapor Pressure of a SolutionContaining a Nonvolatile SoluteIdeal solutions• obey Raoult’s law exactly• solute-solute, solvent-solvent, and solute-solventinteractions are identical• do not existReal Solutions• are nonideal• may approach ideal behaviorif solute and solvent aresimilar• Example: sucrose in water
Vapor Pressure of an Ideal SolutionTwo Volatile SolventsPtotal = PA + PB = XAPA0 + XBPB0
Raoult’s Law Vapor Pressure for a Solutionof Two Volatile LiquidsIDEALSOLUTIONNONIDEAL SOLUTIONSPositiveDeviationNegativeDeviation
Colligative PropertiesDepend only on the number, not on the identity, of thesolute particles in an ideal solution. Boiling point elevation Freezing point depression Osmotic pressureBoiling Point ElevationKb = Molal boiling point elevation constantm = Molality of the soluteA nonvolatile solute elevates the boiling point of the solvent.T = Kbmsolute
Freezing Point DepressionKf = Molal freezing point depressionconstantm = Molality of the soluteA nonvolatile solute depresses the freezing point of the solvent.T = KfmsolutePhase Diagram for an Aqueous SolutionIn effect, a dissolvedsolute acts to extendthe liquid range ofthe solvent
Colligative Properties of Electrolyte SolutionsT = imK= iMRTi =moles of particles in solutionmoles of solute dissolvedvan’t Hoff factor, “i”, relates to the number of ions per formulaunit.NaCl = 2, K2SO4 = 3Data for 0.05 m SolutionsElectrolyte i (expected) i (observed)NaCl 2.0 1.9MgCl2 3.0 2.7FeCl3 4.0 3.4
Osmosis Some substances form semipermeable membranes, allowingsome smaller particles to pass through, but blocking otherlarger particles. In biological systems, most semipermeable membranes allowwater to pass through, but solutes are not free to do so.
In osmosis, there is net movement of solvent from the area ofhigher solvent concentration (lower solute concentration) tothe are of lower solvent concentration (higher soluteconcentration).Osmosis• The pressure required to stop osmosis, known asosmotic pressure, , iswhere M is the molarity of the solutionIf the osmotic pressure is the same on both sides of a membrane(i.e., the concentrations are the same), the solutions are isotonicnV= ( )RT = MRTOsmotic Pressure
Colloids Colloids are particles that are large on the molecular scale but stillsmall enough to remain suspended indefinitely in a solvent system.(aka colloidal dispersions.) They are intermediate between solutions and heterogeneousmixtures. They have the ability to scatter light; known as the Tyndall effect.Hydrophilic and Hydrophobic Colloids The most important colloids are those in which water is thesolvent, or dispersing agent. Hydrophilic colloids are water loving and are found in thehuman body and help keep molecules suspended in water.(enzymes, antibodies) Hydrophobic colloids are water fearing and must be stabilizedbefore they can be mixed into water. (droplets of oil.)
Colloids in Biological SystemsSome molecules have apolar, hydrophilic (water-loving) end and anonpolar, hydrophobic(water-hating) end.Call us for more information:www.iTutor.com1-855-694-8886VisitThe End
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