2The solute is NaCl(s) and the solvent is H2O(l). DefinitionsA solution is a homogeneous mixture of a solute dissolved in a solvent.The solvent is generally in excess an aqueous solution has water as solvent.ExampleThe solution NaCl(aq) is sodium chloride NaCl(s) dissolved in water H2O(l)The solute is NaCl(s) and the solvent is H2O(l).Air is an example of a solution with one “solvent” (nitrogen) and many “solutes” (oxygen, helium, argon, carbon dioxide, etc.)
4Definitions Solutions can be classified as saturated or unsaturated. Solutions can be classified as saturated or unsaturated.A saturated solution contains the maximum quantity of solute that dissolves at that temperature.A saturated solution represents equilibrium: rate of dissolving equals to rate of crystallizationAn unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperatureA SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved
5Supersaturated solutions are unstable. The supersaturation is only temporary, and usually accomplished in one of two ways:Warm the solvent so that it will dissolve more, then cool the solutionEvaporate some of the solvent carefully so that the solute does not solidify and come out of solution.
7Electrolyte and Non-electrolyte Electrolyte and Non-electrolyteElectrolyte: a substance that conducts electricity when dissolved in water.Acids, bases and soluble ionic solutions are electrolytes.Non-electrolyte: a substance that does not conduct electricity when dissolved in water.Molecular compounds and insoluble ionic compounds are non-electrolytes.
8Some solutes can dissociate into ions. ElectrolytesSome solutes can dissociate into ions.Electric charge can be carried.
9Types of solutes Strong Electrolyte - 100% dissociation, Types of soluteshigh conductivityStrong Electrolyte -100% dissociation,all ions in solutionNa+Cl-
10Types of solutes Weak Electrolyte - partial dissociation, Types of solutesslight conductivityWeak Electrolyte -partial dissociation,molecules and ions in solutionCH3COOHCH3COO-H+
11Types of solutes Non-electrolyte - No dissociation, Types of solutesno conductivityNon-electrolyte -No dissociation,all molecules in solutionsugar
12Strong electrolyte dissociates completely. Types of ElectrolytesStrong electrolyte dissociates completely.Good electrical conduction.Weak electrolyte partially dissociates.Fair conductor of electricity.Non-electrolyte does not dissociate.Poor conductor of electricity.A generalization is helpful:Essentially all soluble ionic compounds are strong electrolytes.Most molecular compounds are weak electrolytes or non-electrolytes
13→ A strong electrolyte: MgCl2(s)+H2O → Mg2+(aq) + 2 Cl- (aq) Representation of Electrolytes using Chemical EquationsA strong electrolyte:MgCl2(s)+H2O → Mg2+(aq) + 2 Cl- (aq)A weak electrolyte:CH3COOH(aq) ← CH3COO -(aq) +H+(aq)→Strong – complete dissociationWeak – reversibleCH3OH(aq)A non-electrolyte:
14Strong acids: HNO3, H2SO4, HCl, HClO4 Strong ElectrolytesStrong acids: HNO3, H2SO4, HCl, HClO4Strong bases: MOH (M = Na, K, Cs, Rb etc)Salts: All salts dissolving in water are completely ionized.Stoichiometry & concentration relationshipNaCl (s) +H2O Na+ (aq) + Cl– (aq)Ca(OH)2 (s) +H2O Ca2+(aq) + 2 OH– (aq)AlCl3 (s) +H2O Al3+ (aq) Cl– (aq)(NH4)2SO4 (s) +H2O 2 NH4 + (aq) + SO42– (aq)
15Interaction of Solute & Solvent 3 Stages of Solution ProcessSeparation of Solutemust overcome IMF(Intermolecular forces) or ion-ion attractions in soluterequires energy, ENDOTHERMIC ( + DH)Separation of Solventmust overcome IMF of solvent particlesrequires energy, ENDOTHERMIC (+ DH)Interaction of Solute & Solventattractive bonds form between solute particles and solvent particles“Solvation” or “Hydration” (where water = solvent)releases energy, EXOTHERMIC (- DH)
16Consider the dissolution of NaOH in H2O Dissolution at the molecular level?Consider the dissolution of NaOH in H2O
181. Nature of Solute / Solvent- Like dissolves like (IMF) Factors Affecting Solubility1. Nature of Solute / Solvent- Like dissolves like (IMF)2. Temperature -i) Solids/Liquids- Solubility increases with TemperatureIncrease K.E. increases motion and collision between solute / solvent.ii) Gas - Solubility decreases with TemperatureIncrease K.E. result in gas escaping to atmosphere.3. Pressure Factor -i) Solids/Liquids - Very little effectSolids and Liquids are already close together, extra pressure will not increase solubility.ii) gas - Solubility increases with Pressure.Increase pressure squeezes gas solute into solvent.
20http://www.authorstream.com/Presentation/Margot- Solubility curve Any solution can be made saturated, unsaturated, or supersaturated by changing the temperature.
21Solubilities of Solids vs TemperatureSolubilities of several ionic solid as a function of temperature. MOST salts have greater solubility in hot water.A few salts have negative heat of solution, (exothermic process) and they become less soluble with increasing temperature.
22http://www.authorstream.com/Presentation/Margot- The rate of solution The rate of solution is a measure of how fast a substance dissolves. Some of the factors determining the rate of solution are:size of the particles -- When a solute dissolves, the action takes place only at the surface of each particle. When the total surface area of the solute particles is increased, the solute dissolves more rapidly. Breaking a solute into smaller pieces increases its surface area and hence its rate of solution.(Sample problem: a cube with sides 1.0 cm long is cut in half, producing two pieces with dimensions of 1.0 cm x 1.0 cm x 0.50 cm. How much greater than the surface area of the original cube is the combined surface areas of the two pieces?2.0 cm2
23http://www. authorstream The rate of dissolutionstirring -- With liquid and solid solutes, stirring brings fresh portions of the solvent in contact with the solute, thereby increasing the rate of solution.amount of solute already dissolved -- When there is little solute already in solution, dissolving takes place relatively rapidly. As the solution approaches the point where no solute can be dissolved, dissolving takes place more slowly.temperature -- For solid, liquid and gaseous solutes, changing the temperature not only changes the amount of solute that will dissolve but also changes the rate at which the solute will dissolve.
24Temperature & the Solubility of Gases The solubility of gases decreases at higher temperatures WHY???
25The effect of partial pressure on solubility of gases Henry’s LawAt pressure of few atmosphere or less, solubility of gas solute follows Henry Law which states that the amount of solute gas dissolved in solution is directly proportional to the amount of pressure above the solution.c = k Pc = solubility of the gas (M)k = Henry’s Law ConstantP = partial pressure of gasHenry’s Law Constants (25°C), kN •10-7 M/mmHgO •10-6 M/mmHgCO •10-5 M/mmHg
26How does Henry’s Law apply?? & Soft Drinks Henry’s Law & Soft DrinksSoft drinks contain “carbonated water” – water with dissolved carbon dioxide gas.The drinks are bottled with a CO2 pressure greater than 1 atm.When the bottle is opened, the pressure of CO2 decreases and the solubility of CO2 decreases, according to Henry’s Law.Therefore, bubbles of CO2 escape from solution.
27Colligative Properties On adding a solute to a solvent, the properties of the solvent are modified.Vapor pressure decreasesMelting point decreasesBoiling point increasesOsmosis 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.
28Vapor Pressure Lowering for a SolutionThe diagram below shows how a phase diagram is affected by dissolving a solute in a solvent. Notice the changes in the freezing & boiling points.
29http://www.wsd1.org/grantpark/staff/patenaude/powerpoint/Solutions_30SE.ppt Vapor Pressure Lowering The presence of a non-volatile solute means that fewer solvent particles are at the solution’s surface, so less solvent evaporates!
30PA = vapour pressure of solvent A above solution Raoult’s Law Describes vapor pressure lowering mathematicallyThe lowering of the vapour pressure when a non-volatile solute is dissolved in a volatile solvent (A) can be described by Raoult’s Law:PA = cAP°APA = vapour pressure of solvent A above solutionXA = mole fraction of the solvent A in solution.P°A = vapour pressure of pure solvent A .only the solvent (A) contributes tothe vapour pressure of the solution
31Mixtures of Volatile Liquids Both liquids evaporate & contribute to the vapor pressure
32Raoult’s Law: Mixing Two Volatile LiquidsSince BOTH liquids are volatile and contribute to the vapour, the total vapor pressure can be represented using Dalton’s Law:PT = PA + PBThe vapor pressure from each component follows Raoult’s Law:PT = cAP°A + cBP°BAlso, cA + cB = (since there are 2 components)Ideal solutions obtained if solute-solute, solute-solvent,and solvent-solvent interactions are similar,i.e. ΔHsoln = 0.
33Deviations from ideality occur if, , there are strong solute-solvent Deviations from ideality occur if, , there are strong solute-solventinteractions as may be in H-bonding between solute and solvent.Such solutions are called nonideal solutions.― Deviations from Raoult’s lawΔHsoln << 0 ⇒ negative deviationΔHsoln >> 0 ⇒ positive deviationBenzene - Toluene mixture:The vapor pressure from each component follows Raoult's Law.Recall that with only two components, Bz + Tol = 1Benzene: when Bz = 1, PBz = P°Bz = 384 torr &when Bz = 0 , PBz = 0Toluene: when Tol = 1, PTol = P°Tol = 133 torr & when Tol = 0, PBz = 0
35Normal Boiling Point: BP of Substance @ 1atm Normal Boiling ProcessNormal Boiling Point: BP of 1atmWhen solute is added , BP > Normal BPBoiling point is elevated when solute inhibits solvent from escaping.
36ΔTb = (Tb -Tb°) = i ·m ·kb Where, ΔTb = BP. Elevation Boiling Point ElevationΔTb = (Tb -Tb°) = i ·m ·kbWhere, ΔTb = BP. ElevationTb = BP of solvent in solutionTb° = BP of pure solventm = molality , kb = BP ConstantSome Boiling Point Elevation and Freezing Point Depression ConstantsNormal bp (°C) Kb Normal fp (°C) KfSolvent pure solvent (°C/m) pure solvent (°C/m)WaterBenzeneCamphorChloroform(CH3Cl)
37Boiling Point Elevation and Freezing Point Depression ∆T = i K mi = van’t Hoff factor = number of particles per molecule/formula unit.For covalent compounds, i = 1.For ionic compounds, i = the number of ionsCompound Theoretical Value of iglycolNaCl 2CaCl2 3Ca3(PO4)2 5
38Normal Freezing Point: FP of Substance @ 1atm Freezing Point DepressionNormal Freezing Point: FP of 1atmWhen solute is added, FP < Normal FPFP is depressed when solute inhibits solvent from crystallizing.When solution freezes the solid form is almost always pure.Solute particles does not fit into the crystal lattice of the solvent because of the differences in size. The solute essentially remains in solution and blocks other solvent from fitting into the crystal lattice during the freezing process.
39Phase Diagram and the lowering of the freezing point. Freezing Point DepressionTf = i ·m ·kfWhere, Tf = FP depressioni = van’t Hoff Factorm = molality , kf = FP ConstantGenerally freezing point depression is used to determine the molar mass of an unknown substance.Derive an equation to find molar mass from the equation above.Phase Diagram and the lowering of the freezing point.
40http://www.wsd1.org/grantpark/staff/patenaude/powerpoint/Solutions_30SE.ppt Osmotic pressure Osmosis is the spontaneous movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentrationOsmotic Pressure - The Pressure that must be applied to stop osmosisP = i CRTwhere P = osmotic pressurei = van’t Hoff factorC = molarityR = ideal gas constantT = Kelvin temperature
41http://www.wsd1.org/grantpark/staff/patenaude/powerpoint/Solutions_30SE.ppt Osmosis and Blood Cells (a) A cell placed in an isotonic solution. The net movement of water in and out of the cell is zero because the concentration of solutes inside and outside the cell is the same.(b) In a hypertonic solution, the concentration of solutes outside the cell is greater than that inside. There is a net flow of water out of the cell, causing the cell to dehydrate, shrink, and perhaps die.(c) In a hypotonic solution, the concentration of solutes outside of the cell is less than that inside. There is a net flow of water into the cell, causing the cell to swell and perhaps to burst.