Presentation on theme: "Solutions Entry Task: Nov 19 th Monday Question: What are the 2 components that make up a solution? You have 5 minutes."— Presentation transcript:
Solutions Entry Task: Nov 19 th Monday Question: What are the 2 components that make up a solution? You have 5 minutes
Solutions Agenda: Sign off discuss Ch. 13 sec. 1-3 reading In-class solubility curve HW: Pre-Lab Solutions
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.
Solutions BREAK OUT AP EQUATION SHEET These formulas are rarely or not at all on the AP Exam Density of gas Root mean Speed of gas Kinetic energy of gas molecules and moles of gas Grahams Law Osmotic pressure and Beers Law
Solutions 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.
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.
Solutions 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
Solutions 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 NH 4 NO 3 in water, heat is absorbed, not released.
Solutions 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.
Solutions Student, Beware! Just because a substance disappears when it comes in contact with a solvent, it doesnt mean the substance dissolved. It may have reacted.
Solutions Student, Beware! Dissolution is a physical changeyou can get back the original solute by evaporating the solvent. If you cant get it back, the substance didnt dissolve, it reacted.
Solutions Types of Solutions Saturated 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.
Solutions 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.
Solutions 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.
Solutions Factors Affecting Solubility
Solutions 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.
Solutions Gases in Solution In general, the solubility of gases in water increases with increasing mass. Larger molecules have stronger dispersion forces.
Solutions Gases in Solution – Henrys 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. C g = kP g where C g is the solubility of the gas; k is the Henrys law constant for that gas in that solvent; P g is the partial pressure of the gas above the liquid.
Solutions Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.
Solutions Temperature The opposite is true of gases: Carbonated soft drinks are more bubbly if stored in the refrigerator. Warm lakes have less O 2 dissolved in them than cool lakes.
Solutions Solubility Chart What is the solubility of KNO 3 at 30ºC? ~45 grams of KNO 3 What temperature will 50 grams of KCl dissolve? ~75°C If I add 30 grams of K 2 Cr 2 O 7 at 60°C, what type of solution do we have? Unsaturated How much more solute can we add to make it saturated? If the temperature increased from 60ºC to 80ºC, how much more K 2 Cr 2 O 7 can be added? ~less than 10 grams = 20 more grams
Solutions 4. Rank the following solutions, KCl in water, CH 2 Cl 2 in benzene, C 6 H 6, methanol, CH 3 OH, 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 CH 2 Cl. Methanol has hydrogen bonding and would dissolve in water. KCl being ionic would have a ion-dipole attraction and would readily dissolve in water
Solutions 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. H 1 is solute to solute (NH 4 + NO 3 - ) <0 H 2 is solvent to solvent (H 2 O H 2 O ) <0 H 3 is solvent to solute (NH 4 + NO 3 - H 2 O ) >0 When the overall process requires MORE energy into the system then the dissolution process then its endothermic
Solutions 8. The enthalpy of solution of KBr in water is about 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.
Solutions 13.9 The solubility of Cr(NO 3 ) 3 9H 2 O 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.
Solutions Which of the following in each pair is likely to dissolve in hexane, C 6 H 14 : a) C 6 H 12 or C 6 H 12 O 6 ; b) CH 3 CH 2 COOH or CH 3 CH 2 COONa; c) HCl or CH 3 CH 2 Cl. Explain each case. a) C 6 H 12 or C 6 H 12 O 6 ; because its nonpolar – like hexane b) CH 3 CH 2 COOH or CH 3 CH 2 COONa; The propionic acid does have H-bonding but its weaker than the ion-ion IMF c) HCl or CH 3 CH 2 Cl. The hydrocarbon group at the end has dispersion forces
Solutions In-class Solubility Chart
Solutions PRACTICE: 1.What is the solubility of K 2 Cr 2 O 7 at 30°C?_______ 2.What temperature will 20 grams of KCl dissolve?_____ 3.If I add 40 grams of Pb(NO 3 ) 2 at 40°C, what type of solution do we have? 4.How much more solute can we add to make it saturated? 5.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
Solutions 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 = 14 g = 60 grams
Solutions 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? YOUR TURN: 55g-75g = 20g 45g – 13g = 32g 76/2 = 38 g
Solutions 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? YOUR TURN: 34g x 10% = 3.4g 46-13g/2 = 16.5g At 0ºC 27 grams x 2 = 54g at 85ºC