Entry Task: Nov 19th Monday Question: What are the 2 components that make up a solution? You have 5 minutes

Agenda: Sign off discuss Ch. 13 sec. 1-3 reading In-class solubility curve HW: Pre-Lab Solutions

I can… Explain the components and physical/chemical processes of a solution Describe and interpret solubility curves of a substance. State the factors that affect the solubility of a solute in solution.

BREAK OUT AP EQUATION SHEET Density of gas Root mean Speed of gas Kinetic energy of gas molecules and moles of gas Grahams Law Osmotic pressure and Beers Law These formulas are rarely or not at all on the AP Exam

Chapter 13 Properties of Solutions

Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed uniformly throughout the solvent.

Solutions The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

How Does a Solution Form? As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them. © 2012 Pearson Education, Inc.

Energy Changes in Solution Three processes affect the energetics of the process: Separation of solute particles Separation of solvent particles New interactions between solute and solvent The enthalpy change of the overall process depends on H for each of these steps.

Energy Changes in Solution Three processes affect the energetics of the process: Separation of solute particles Separation of solvent particles New interactions between solute and solvent

Why Do Endothermic Processes Occur? Things do not tend to occur spontaneously (i.e., without outside intervention) unless the energy of the system is lowered. Yet we know that in some processes, like the dissolution of NH4NO3 in water, heat is absorbed, not released.

Enthalpy Is Only Part of the Picture The reason is that increasing the disorder or randomness (known as entropy) of a system tends to lower the energy of the system. So even though enthalpy may increase, the overall energy of the system can still decrease if the system becomes more disordered.

Student, Beware! Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. It may have reacted.

Student, Beware! Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t get it back, the substance didn’t dissolve, it reacted.

Types of Solutions Saturated Unsaturated Solvent holds as much solute as is possible at that temperature. Dissolved solute is in dynamic equilibrium with solid solute particles. Unsaturated Less than the maximum amount of solute for that temperature is dissolved in the solvent.

Types of Solutions Supersaturated Solvent holds more solute than is normally possible at that temperature. These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

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. The more similar the intermolecular attractions, the more likely one substance is to be soluble in another.

Factors Affecting Solubility

Factors Affecting Solubility Glucose (which has hydrogen bonding) is very soluble in water, while cyclohexane (which only has dispersion forces) is not. Vitamin A is soluble in nonpolar compounds (like fats). Vitamin C is soluble in water.

Gases in Solution In general, the solubility of gases in water increases with increasing mass. Larger molecules have stronger dispersion forces.

© 2012 Pearson Education, Inc. Gases in Solution The solubility of liquids and solids does not change appreciably with pressure. But the solubility of a gas in a liquid is directly proportional to its pressure. Start here 1/21/10--8:30 & 10 © 2012 Pearson Education, Inc.

Gases in Solution – Henry’s Law The solubility of liquids and solids does not change appreciably with pressure. The solubility of a gas in a liquid is directly proportional to its pressure. Cg = kPg where Cg is the solubility of the gas; k is the Henry’s law constant for that gas in that solvent; Pg is the partial pressure of the gas above the liquid.

Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

Temperature The opposite is true of gases: Carbonated soft drinks are more “bubbly” if stored in the refrigerator. Warm lakes have less O2 dissolved in them than cool lakes.

Solubility Chart What is the solubility of KNO3 at 30ºC? ~45 grams of KNO3 What temperature will 50 grams of KCl dissolve? ~75°C If I add 30 grams of K2Cr2O7 at 60°C, what type of solution do we have? Unsaturated How much more solute can we add to make it saturated? ~less than 10 grams If the temperature increased from 60ºC to 80ºC, how much more K2Cr2O7 can be added? 58-38 = 20 more grams

4. Rank the following solutions, KCl in water, CH2Cl2 in benzene, C6H6, methanol, CH3OH, in water, in terms of increasing magnitude of solvent-solute interaction, and indicate the principal type of interaction in each case. The benzene has dispersion forces and the interactions with CH2Cl. Methanol has hydrogen bonding and would dissolve in water. KCl being ionic would have a ion-dipole attraction and would readily dissolve in water

5. The dissolution of ammonium nitrate in water is an endothermic process. Describe the solution process on terms of three distinct components, and show how the sum of these can be a net positive overall. ∆H1 is solute to solute (NH4+ NO3-) <0 ∆H2 is solvent to solvent (H2O H2O ) <0 ∆H3 is solvent to solute (NH4+ NO3- H2O ) >0 When the overall process requires MORE energy into the system then the dissolution process then its endothermic

8. The enthalpy of solution of KBr in water is about +19. 8 kJ/mol 8. The enthalpy of solution of KBr in water is about +19.8 kJ/mol. The process, then, is endothermic. Nevertheless, the solubility of KBr in water is relatively high. Why does the solution process, although endothermic, proceed? There must be a stronger attraction between the water and potassium and water and bromide than for each other and a greater need for disorder. So energy is required for this process- endothermic.

13.9 The solubility of Cr(NO3)3 •9H2O in water is 208g per 100g of water at 15°C. A solution was prepared by dissolving 324 g per 100g of water at 35°C. When this solution slowly cooled to 15°C , no precipitate forms. A) What term describes this solution? B) What action might you take to cause crystallization from the solution? As you heat the solution, you increase the solubility making it super saturated. If you seed (add a crystal of solute), the solution will crystalize and precipitate out.

13.16 Which of the following in each pair is likely to dissolve in hexane, C6H14: a) C6H12 or C6H12O6; b) CH3CH2COOH or CH3CH2COONa; c) HCl or CH3CH2Cl. Explain each case. a) C6H12 or C6H12O6; because its nonpolar – like hexane b) CH3CH2COOH or CH3CH2COONa; The propionic acid does have H-bonding but its weaker than the ion-ion IMF c) HCl or CH3CH2Cl. The hydrocarbon group at the end has dispersion forces

In-class Solubility Chart

PRACTICE: What is the solubility of K2Cr2O7 at 30°C?_______ What temperature will 20 grams of KCl dissolve?_____ If I add 40 grams of Pb(NO3)2 at 40°C, what type of solution do we have? How much more solute can we add to make it saturated? If the temperature increased from 60ºC to 80ºC, how much more NaCl can be added? 15 g There is none Unsaturated 35 grams ~2-3 grams

YOUR TURN: 6. What is the minimum temperature needed to dissolve 35 grams of potassium chloride in 100 grams of water?   7. At what temperature do potassium chloride and potassium nitrate have the same solubility? 8. If 250 grams of potassium dichromate are mixed with 100 grams of water at 85°C, how much will not dissolve? 9. If 15 grams of potassium nitrate are added to 100 grams of water at 30 °C, how much more must be added to saturate the solution? 30°C ~22°C 63-77 = 14 g 15-75 = 60 grams

YOUR TURN: 10. A 100 grams of water at 20 °C are saturated with lead II nitrate. If this solution is heated to 40 °C; how much more can be dissolved?   11. A 100 grams of water at 90 °C are saturated with potassium chlorate. If this solution is cooled to 35°C, how much of the solid will precipitate? 12. How much lead II nitrate will dissolve in 50 grams of water at 40°C? 55g-75g = 20g 45g – 13g = 32g 76/2 = 38 g

YOUR TURN: 13. How much sodium nitrate will dissolve in 10 grams of water at 10 °C?   14. If 50 grams of water are saturated at 90 °C with potassium chlorate and then cooled to 40°C, how much will precipitate? 15. What temperature is needed to dissolve twice as much potassium chloride as can be dissolved at 0 °C in 100 grams of water? 34g x 10% = 3.4g 46-13g/2 = 16.5g At 0ºC 27 grams x 2 = 54g at 85ºC

HW: Ch. 13 sec 4-5 notes