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Chapter 15

Chapter 15. Solutions. Obj. 1-2…Vocabulary. solution :. homogenous mixture. ~ smallest particles. ~ no Tyndall effect. ~ won’t settle out. ~ composed of solute and solvent. does the dissolving. gets dissolved. ** always more solvent than solute! **.

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Chapter 15

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  1. Chapter 15 Solutions

  2. Obj. 1-2…Vocabulary • solution: homogenous mixture ~ smallest particles ~ no Tyndall effect ~ won’t settle out ~ composed of solute and solvent does the dissolving gets dissolved ** always more solvent than solute! ** • name the solute/solvent in the following solutions… solvent solute salt water salt water atmosphere other gases N2 brass Zn Cu (Zn and Cu)

  3. Obj. 1-2 cont… • solubility: the amount of solute that will dissolve in a solvent at a given temperature. • miscible: liquids that are capable of dissolving each other. (alcohol and water) • immiscible: liquids that are insoluble in each other… they ‘don’t mix’. (oil and water) • solvation: the process that occurs as an ionic solute dissolves. ~ solute breaks apart (dissociates) into cation (+) and anion(-). ~ solvent particles surround individual ions ~ WILL NOT occur if ionic bonds are stronger than their attraction to the solvent.

  4. Obj. 1-2 cont… • hydration: solvation in which water is the solvent.

  5. Obj. 3…Solvation Rules • in order for solvation to occur, a solute must be broken apart and surrounded by solvent particles. • use the rule ‘like dissolves like’ to predict whether solvation will occur. starts w/ metal (cation) ~ polar (ionic) solvents dissolve polar solutes ~ non-polar (covalent) solvents dissolve non-polar solutes starts w/ non-metal • will solvation occur in the following examples?!?! no yes ~ P2O5 and H2O ~ NaCl and H2O no yes ~ CCl4 and C6H6 ~ KCl and C6H6

  6. Obj. 4-5…Solvation of Solids and Gases • In general, chemical rxns. are more likely to occur if they are exothermicand increasing in entropy. • an exothermic reaction releases thermal energy to the environment. • an endothermic reaction absorbs thermal energy from the environment. • entropy(ΔS) is a measure of disorder of a system. All natural processes tend to increase in entropy. ~ high entropy = more disorder Ex… solid gas Rxns. w/ more products than reactants! low ΔS high ΔS high ΔS

  7. Obj. 4-5 cont… • The problem with solids… • the solvation of solids is an endothermic process dissociation (seperation into ions) requires energy! • The solution… • Must contain huge amounts of entropy in order to occur spontaneously. ~ one salt crystal dissociates into millions of ions!

  8. Obj. 4-5 cont… • The problem with gases… • the solvation of a gas requires a decrease in entropy (liquids have less entropy than gases) • The solution… • Reactions must be largely exothermic in order to occur spontaneously.

  9. Obj. 6…How Pressure & Temperature Affect Solvation • IN GENERAL…solubility rate of temp ↑ causes solubility ↑ solid in a liquid: (sugar is more soluble in hot tea than iced tea) • IN GENERAL…solubility rate of a • gas in a liquid: temp ↑ causes solubility ↓ warm soft drinks quickly go ‘flat’ pressure ↑ causes solubility ↑ CO2 forced into solution in an unopened soda – what happens when it is opened?

  10. Obj. 7…Factors Affecting Solubility • Important factors affecting solubility rates… ~ particle size/surface area (smaller = more soluble) ~ agitation/stirring (more agitation = more soluble) ~ temperature (depends on solute) gases like cold solids like hot

  11. Obj. 10…Dilute vs. Concentrated • concentrated solutions contain a high amount of solute. ~ ‘strong’ • diluted solutions contain a low amount of solute. ~ ‘weak’ • These terms are not very helpful when describing solution concentration b/c they are completely relative. • 1 gram of solute compared to 10 grams = dilute • 1 gram of solute compared to 0.1 grams = concentrated

  12. Obj. 11…Types of Solutions • unsaturated solutions contain a less solute than they are capable of dissolving at a given T and P. ~ can hold more…not full yet! • saturated solutions contain the max. amount of solute that they are capable of dissolving at a given T and P. ~ equilibrium exists b/n dissolved and undissolved solute. ~ completely full, can’t hold any more! • supersaturated solutions contain more solute(dissolved) than it is supposed to hold at a given T and P. ~ must heat solution up to allow more solute to dissolve ~ then let it cool down very slowly, undisturbed.

  13. Obj. 11 cont… • a solubility curve shows saturated solutions of given substances at given temps. ~ any coordinate below this curve = unsaturated ~ any coordinate above this curve = supersaturated

  14. Obj. 11 cont… NaNO3 • Which substance is most soluble at 40°C? ~ 50 grams • How many grams of NH4Cl will dissolve at 50°C? KNO3 and • What two substances have the same solubility at 24°C? Yb2(SO4)3 • If you place 70 grams of KBr into 100g of water at 60°C, what unsaturated type of solution have you made? • How many grams of NaNO3 will dissolve in 300.0g of water at ~ 240 grams (80 x 3) 10.0°C?

  15. Obj. 8…Precipitates • precipitate: an insoluble solid that will separate from a solution during a reaction (double displacement). ~ using solubility rules, we can predict precipitates.

  16. Obj. 8 cont… • Predict the precipitate… *precipitate* +1 -1 +1 -1 LiNO3+ AgI LiI (aq) + AgNO3(aq) (s) (aq) *precipitate* +1 -1 -2 +3 6NaOH (aq) + Cr2(SO4)3(aq) 3Na2SO4+ 2Cr(OH)3 (aq) (s)

  17. Obj. 9…Net Ionic Equations • a net ionic equationshows the chemical change in a solution (formation of precipitate). ~ all soluble (aq) compounds are separated into ions. ~ insoluble (s) compounds are written as compounds. • To write… ~ write the complete ionic equation. • separate (aq) compounds. • leave (s) compounds intact. ~ cross out any spectator ions… • ions that appear on both sides of equation.

  18. Obj. 9 cont… • Ex… LiI (aq) + AgNO3(aq) LiNO3(aq) + AgI (s) • write complete ionic equation… Li+1 + I-1 + Ag+1 + AgI (s) NO3-1 Li+1 + NO3-1 + • cross out spectator ions… • what is left is the net ionic equation! I-1 + Ag+1 AgI (s) • Ex… 6NaOH (aq) + Cr2(SO4)3(aq) 3Na2SO4(aq)+ 2Cr(OH)3(s) 6Na+1+ 6OH-1+ 2Cr+3+ 2Cr(OH)3(s) 3SO4-2 6Na+1+ 3SO4-2+ 6OH-1 + 2Cr+3 2Cr(OH)3(s)

  19. Obj. 12-13…Solution Calculations • we said that ‘dilute’ and ‘concentrated’ are very general terms for solution concentration. • Molarityindicates how many moles of solute are dissolved in one liter of solution. moles ~ molarity = ~ units = M Liters • Ex… What is the molarity of a salt water solution containing 9.0 moles of salt dissolved in 3.0 liters of solution? 9.0 moles = 3.0 M 3.0 liters

  20. Obj. 12-13 cont… • Ex… 23 35 What is the molarity of 174 grams of NaCl dissolved in 500.0 mL of solution? moles ~ molarity = Liters 174 grams 1 mole 1000 mL = 500.0 mL 1 liter 58 grams NaCl 6.00 M

  21. Obj. 12-13 cont… • Molalityindicates how many moles of solute are dissolved in one kilogram of solvent. moles ~ molality = ~ units = m Kg • Ex… 59 160 What is the molality of 199 grams of NiBr2 in 500.0 grams of water? 199 grams NiBr2 1 mole 1000 grams = 500.0 grams 219 grams NiBr2 1 Kg 1.82 m

  22. Obj. 12-13 cont… • Other types of solution concentration include… part mass of solute or solvent ~ % mass = = x 100 whole mass of solution part (solute) • Ex… What is the % by mass of 62.0 grams of KCl dissolved in 475 grams of water? solvent part % mass = whole ** whole = solution… solute + solvent! 62.0 + 475 = 537grams of solution 62.0 % mass = = x 100 11.5% 537

  23. Obj. 12-13 cont… part (solute) whole (solution) • Ex… How many grams of KOH are required to prepare 450.0 grams of a 30.0% solution? % part x % mass = x whole whole part = % x whole whole = x KOH = 0.300 450.0 135 g ~ pph = parts per hundred ~ ppt = parts per thousand parts per million ~ ppm =

  24. Obj. 12-13 cont… • Dilution calculations… ~ a dilution = a solution is made less concentrated (weaker) by adding more solvent. • changes concentration (molarity). • changes volume of solution. M1V1 = M2V2 initial molarity final molarity initial volume final volume

  25. Obj. 12-13 cont… M1 • Ex… V1 • How many liters of a 12M solution are needed to create 2.0 liters of a 4.0M solution? M1V1 = M2V2 M2 V2 8.0 12 X = 12 X = (4.0) 2.0 0.67 liters X= 12 12 V1 • Ex… M1 • What is the molarity of 1.5 liters of solution made from 600.0 mL of 10.0M NaOH? M2 V2 6.0 1.5 X = 4.0M 1.5 X = (10.0) X= 0.6 1.5 1.5

  26. Obj. 12-13 cont… • Some dilution problems may contain % concentrations instead of molarity… ~ you do NOT have to put % in decimal form…just be consistent! %1 • Ex… mass1 • How many grams of a 25.0% solution of a KCl are needed to prepare 85.0 grams of a 40.0% solution? %2 mass2 %1mass1 = %2mass2 25 X 3400 (40) 25 X = 85 136 grams = X= 25 25

  27. Obj. 14…Colligative Properties • Colligative properites are properties of solutions that are affected only by the # of particles in the solution. • NOT affected by the type of particle!!! • Ex… ~ vapor pressure (VP) ~ freezing point (FP) ~ boiling point (BP)

  28. Obj. 15…Effect of Solutes on Vapor Pressure • Vapor pressure (VP) is the P exerted at the surface of a liquid by particles trying to escape the liquid.

  29. Obj. 15 cont… • adding a nonvolatile solute to a solvent will cause the VP of the solvent to decrease. ~ solute particles replace some solvent particles at the surface of the solution. ~ less solvent particles on surface = less evaporation = lower VP!

  30. Obj. 16 and 18…How Solutes Affect BP and FP • Boiling pt. (BP) is temp. at which the VP of the liquid = atmospheric pressure. ~ adding solute lowers VP of solvent ~ must add more KE (heat) to equalize the pressures ** solutes RAISE the BP of solutions! (i.e. we add salt before we boil water) pure water salt water

  31. Obj. 16 and 18 cont… • Freezing pt. (FP) is temp. at which liquid turns into a solid. ~ enough KE is lost (removal of heat)that molecules stop moving around and lock into place. ~ adding solute lowers VP of solvent ~ even more KE (heat) must be lost to lock molecules into place. ** solutes LOWER the FP of solutions! (i.e. we add salt to icy roads…salt is used in making ice cream )

  32. = Al+3 = Cl-1 glucose Obj. 16 and 18 cont… • Ionic solutes lower the VP of solvents more than molecular solutes! ~ ionic solutes dissociate (break up into ions) in solvents. • AlCl3 dissociates into 4 separate ions (1 Al+3 and 3 Cl-1) ~ molecular solutes stay intact in solvents. • glucose (C6H12O6) breaks into separate units of C6H12O6… NOT C’s, H’s and O’s!

  33. Obj. 17…BP and FP Calculations • solutes raise (elevate) the BP of solvents. • to calculate how high the BP is elevated… BP elevation = ΔTBP = m(KBP) + normal BP *given except…* BP constant molality *water = 100°C* *given* • solutes lower (depress) the FP of solvents. • to calculate how low the FP is depressed… FP depression = ΔTFP = normal FP-m(KFP) *given except…* FP constant molality *water = 0°C* *given* ** ionic solutes affect molality!!! ** CaCl2 dissociates into 3 ions, so multiply m by 3! ** Round all temps. to the hundredths place! **

  34. Obj. 17 cont… • Ex… If 52.34 grams of NiBr2 dissolve in 392.0 grams of water, what is the BP of the resulting solution? BP = m(KBP) + normal BP 52.34 g NiBr2 1 mole 1000 g x3= 1.829 m 0.6097 m = 219 g NiBr2 392.0 g water 1 Kg (ions) 0.936 (0.512) + 100°C = 100.94°C BP = 1.829

  35. Obj. 17 cont… • Ex… If 95.67 grams of CCl4 dissolve in 981.0 grams of benzene, what is the FP of the resulting solution? (FP of Benzene = 5.53°C) FP = normal FP-m(KFP) ** molecular, so don’t multiply by anything! 95.67 g CCl4 1 mole 1000 g 0.6416 m = 152 g CCl4 981 g benzene 1 Kg 3.285 2.25°C FP = 5.53°C - 0.6416 (5.12) =

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