Lecture 30 Solutions 4 Read HW BLB 13 1 13 3 BLB 13 7 15 21 23 33 Sup13 1 7 Know how solutions form solubility saturation factors affecting solubility Need help Get help TAs in CRC 211 Whitmore and SI hours on Chem 110 website my office hours Mon 12 30 2 Tues 10 30 12 in 324 Chem Bldg or 326 Chem Bonus deadline for BST 9 Solutions dilutions April 2 Review chemical nomenclature e g BST 5 Lecture 8 memorize those strong acids bases BLB Table 4 2 Check out the grade u lator http courses chem psu edu chem110 spring grade htm Exam 3 Monday April 6 6 30 pm Sign up for the conflict exam if needed Last day to sign up is Wed April 1 No textprogrammable calculators PDAs iPods etc Bring PSU ID and several pencils Late drop deadline Friday April 10 11 59 pm via elion Sheets Page 1 Lecture 30 The solution process solvation solutions form when the attractive IM forces between solute solvent are comparable in magnitude nature to those that exist between solute solute or solvent solvent alone hydration solvation in water for solvation to occur 1 break solute solute interactions 2 break solvent solvent interactions 3 solute solvent interactions form Sheets Page 2 Lecture 30 H1 H2 H3 Sheets Page 3 Lecture 30 The solution process cont processes occur spontaneously when energy is released exothermic H disorder increases entropy S these processes are linked a process can be endothermic when the increase in entropy disorder is large enough this is true for any type of process dissolution reaction etc forming a solution always increases disorder because of mixing thus spontaneity depends on H Hsoln H1 H2 H3 Hsoln overall enthalpy change in forming a solution a solution will form in most cases unless solute solute or solvent solvent interactions are too strong relative to the solute solvent interactions Sheets Page 4 Lecture 30 Dynamic equilibrium dynamic equilibrium no change BUT change is occurring on a molecular level this equilibrium can be a physical change e g vapor pressure or solvation or a chemical change more in Chap 15 forward rate backward rate solute dissolve solution crystallize solvent NOTE vs Sheets Page 5 Lecture 30 Solubility solubility amount of a substance that can be dissolved in solvent under given conditions e g T saturated solution solution that contains the concentration of solute under the given conditions a solution in dynamic equilibrium with undissolved solute additional solute will NOT dissolve if added to the solution unsaturated solution solution that contains than maximum concentration of solute more solute can dissolve if added to the solution supersaturated solution solution that contains than maximum concentration of solute more than the equilibrium amount solution is unstable that is NOT at equilibrium Sheets Page 6 Lecture 30 Solubility generalization in general like dissolves like polar solvents dissolve nonpolar solvents dissolve solutes solutes consider IM forces that are broken formed if they are the same then dissolution is likely solubility in water alcohol at 25 C g 100g of H2O CH3OH CH3CH2OH CH3CH2CH2OH CH3CH2CH2CH2OH 8 06 CH3CH2CH2CH2CH2OH 2 82 CH3CH2CH2CH2CH2CH2OH 0 62 as length of hydrocarbon chain solubility of alcohol in water why is this the case Sheets Page 7 Lecture 30 To phase separate or not to phase separate that is the question a mol solute 100 g H2O at 20 C miscible 2 substances dissolve in all proportions immiscible 2 substances that do NOT dissolve in each other to a significant extent examples NaCl in water KCl in hexane sugar polar in water Ni metal in water NH3 in water or hexane in hexane in water Sheets Page 8 Lecture 30 Example Which one of the following will be most soluble in benzene C6H6 l A B C D E Sheets H2O l CH3OH l HCl l CH3CH2OH l heptane C7H16 l Page 9 Lecture 30 Factors that affect solubility other factors T P temperature can either increase or decrease solubility depending on Hsoln for ionic solids solubility for gases solubility Henry s law relationship between solubility of gases with its partial pressure solids liquids not affected why pop umm I mean soda fizzes Cg K H P g Cg Cg on data sheet Sg in BLB solubility of gas in solution phase KH Henry s law constant different for each solute solvent pair varies with temperature Pg partial pressure of gas the solute over solution Sheets Page 10 Lecture 30 Le Chatelier s principle a dynamic equilibrium tends to oppose any change in conditions more about this in Chap 15 so how do T P changes affect solubility anyway 1 pressure as P increases the system tries to reduce P so more gas dissolves 2 temperature as T increases the system tries to reduce T using the solution process to take up heat if Hsoln 0 heat released exothermic e g solute comes out of solution gases if Hsoln 0 heat taken up endothermic solute dissolves more ionic solids Hsoln 0 at saturation for most ionic solids Sheets Page 11 Lecture 30 More examples To increase the solubility of O2 in water need to do which of the following A increase T B decrease T C increase PO2 D decrease PO2 How will the solubility of KClO3 be affected by an increase in pressure Sheets Page 12 Lecture 30 Before next class Read HW BLB 13 5 13 6 BLB 13 9 58 61 67 69 75 Sup13 12 18 Know colligative properties vapor pressure lowering boiling point elevation freezing point depression osmotic pressure colloids Answers p 9 E p 12 top B C bottom KClO3 solubility is not affected by pressure Sheets Page 13 Lecture 30
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