Chapter 14 Solutions and Their Behaviors Pure substance intermolecular forces Solutions Colligative properties Solutions mixture of two or more substances homogenous in a single phase o Solvent substance present in largest amount o Solutes other substance o If one of substances is liquid and all of the others are solids or gases then the liquid is the solvent no matter what the quantities are Alloy mixture of many metals all in solid phase Solution process As solute dissolves solute particles surrounded by solvent particles and spread randomly throughout solution At some point there s high enough concentration of solute particles that they will precipitate when they bump into each other o Dynamic equilibrium while some fall out and precipitate others are being dissolved At his point no more solute can be dissolved in the solvent Clicker the solution is said to be A Concentrated B Saturated C Strong Some solutions generate heat as solute dissolves in solvent Other solutions require heat to dissolved solute particles in solvent This is referred to as the enthalpy of solution Depends on intermolecular forces that are in solid how strong is lattice energy Have to put in enough energy to break lattice energy by separating ions from each other latticeH 821 kJ mol hydrationH 837 kJ mol solnH 16 kJ mol o Heat energy released exothermic Propane CH3CH2CH3 London dispersion forces little bit of energy needed Hexane CH3CH2CH2CH2CH3 London dispersion forces solnH 0 Soda gas particles dissolved in liquid phase Thermodynamics Everything tends toward greater entropy disorder Clicker The enthalpy of solution for sulfur dioxide in water would be A 0 endothermic B 0 C 0 exothermic Hydrogen bonds are stronger than dipole dipole So C is correct Dissolving most gases in water is exothermic High energy in gas dissipate energy very negative solnH Factors Affecting Solubility Temperature impact changes depending on enthalpy of solution If Hsoln 0 decreasing temp increases solubility If Hsoln 0 increasing temp increases solubility Ex Hot coke will fizz more less gases are soluble in liquid phase at higher temperatures Natures of Solutes Solutes ground into powder will dissolve faster than those in large blocks This impacts rate of solubility not the quantity able to dissolve Gases in Liquids As pressure of gas increases solubility of gas increases Henry s law Cap on bottle under pressure some gas particles go into solution to relieve pressure o Lechatellier s principle talk about it later with chemical equilibrium As more gas particles dissolve there are fewer particles in gas phase and therefore a lower pressure Concentrations of Solutions A saturated solution is one where no more of the solvent can be dissolved in solvent Solution can be heated to get more of solute to dissolve then slowly cooled to end up with a solution with more solute dissolved at a temp than is normally possible o Slow helps keep the solute in the solution Result solution supersaturated incredibly tempermental o Disrupt it in any way big or small solute will start to fall out of solution Qualitative terms for concentrations o Concentrated a lot of solute o Dilute very little solute o Strong lot of solute dissolved ex coffee o Weak very little solute same example Concentrated dilute vs Strong weak very different o Strong weak acids strong weak bases Quantiative units allow us to determine exactly how much solute has been dissolved in a given quantity of solution or solvent o Clicker What is the molarity of a solution if 23 0 g of ethanol C2H6O are dissolved in enough water to make 2 0 L of solution The density of the solution is 1 04 g mL Molarity moles solute L solution 23 0 g x 1 mol 46 g 0 5 mol 0 5 mol 2 0 L 0 25 M Clicker What would the molality be for this question Density mass of solution 2000 mL 1 04 g soln 1 0 mL 2080 g soln 2080 g soln 23 g solv 2 057 g 2 057 kg Molality moles solute kg solvent 0 5 mol 2 057 kg 0 24 m Molal solution know how much solute and solvent to measure out Molar solution dissolve solute in a little bit of solvent dilute to get volume As temperature changes mass won t change but density will which means volume is changing Molarity slightly temperature dependent easier to deal with for calculations Molality not temperature dependent at all have to know density for calculations Clicker what is the percent by weight of ethanol in a solution if 23 0 g of ethanol are dissolved in enough water to make 2 0 L of solution The density of the solution is 1 04 g mL w w mass of solutes mass of solution x 100 23 g 2080 g x 100 1 11 Mole fraction number of moles of solute total moles in the system Clicker What is the mole fraction for this question 114 mol H2O 0 5 mol solute 114 5 mol 0 5 mol solute 114 5 mol solution 0 0044 Pre vet percent weight by volume Typical measure of concentration used in medicine w v mass of solute g volume of solution mL x 100 Ex Typical IV bag is 0 9 w v NaCl o Trying to rehydrate and equalize the electrolytes o Needs to be isotonic with your blood o Pure water in your veins will kill you What is the percent weight volume for this question 1 15