Back Bires, 2005 Slide 1 Chapter 13-14: Mixtures and Aqueous Solutions What are they? Where do we find them? How do we describe them? We use solutions all the time

Back Bires, 2005 Slide 2 Soluble versus insoluble Some solids are soluble in water, ie: table salt, NaCl. Soluble means: able to be dissolved. Some solids are soluble in water, ie: table salt, NaCl. Soluble means: able to be dissolved. Soluble ionic solids (made of cation and anion) dissociate into their ions in water. Soluble ionic solids (made of cation and anion) dissociate into their ions in water. Soluble covalent solids (like sugar) dissolve because they are relatively polar. Soluble covalent solids (like sugar) dissolve because they are relatively polar. In a solution, the dissolved particles cannot be easily seen or separated from the solution. In a solution, the dissolved particles cannot be easily seen or separated from the solution. Alloys are solutions of metals! Alloys are solutions of metals!

Back Bires, 2005 Slide 3 Parts of a solution The dissolving medium is the solvent (what does the dissolving…the dissolver) The dissolving medium is the solvent (what does the dissolving…the dissolver) The dissolved substance is the solute (what gets dissolved…the dissolvey) The dissolved substance is the solute (what gets dissolved…the dissolvey) The solute and solvent together form the solution. The solute and solvent together form the solution. Solvents and solutes can be any phase. Solvents and solutes can be any phase. solution

Back Bires, 2005 Slide 4 Special types of mixtures - Suspensions Suspensions Suspensions –mixtures where the solutes particles are very large, so they don’t completely dissolve into their solvent. Solute particles will settle out of the solution if left undisturbed. – this creates two phases. Solute particles will settle out of the solution if left undisturbed. – this creates two phases. Muddy water and Italian salad dressing are good examples of suspensions. Muddy water and Italian salad dressing are good examples of suspensions.

Back Bires, 2005 Slide 5 Special types of mixtures - Colloids Colloids Colloids –mixtures where the solute particle is smaller than particles in a suspension, but not small enough to dissolve. Colloids have two phases: Colloids have two phases: Dispersed phase – the solute Dispersed phase – the solute Dispersing medium – the solvent. Dispersing medium – the solvent. Mayonnaise and hair gel are good examples of colloids. Mayonnaise and hair gel are good examples of colloids. There are 7 types of colloids, found on page 398… There are 7 types of colloids, found on page 398…

Back Bires, 2005 Slide 6 7 Types of Colloids Page 398 Two groups of colloids: Heterogeneous colloids – two phases are clearly seen Homogeneous colloids – appears to be one phase Colloid Type PhasesExample Sol solid in liquid, liquid substance Paint Gel solid in liquid, solid substance Gelatin Foam gas in liquid Whipped cream Liquid Emulsion liquid in liquid Milk, mayonnaise Solid Emulsion liquid in solid Cheese, butter Solid Aerosol solid in gas Smoke Liquid Aerosol liquid in gas Clouds, fog

Back Bires, 2005 Slide 7 The Tyndall Effect The Tyndall effect allows us to distinguish between solutions, colloids, and suspensions. The Tyndall effect allows us to distinguish between solutions, colloids, and suspensions. It works by shining a beam of light into the mixture. If… It works by shining a beam of light into the mixture. If… Light doesn’t pass through Light doesn’t pass through –the mixture is a suspension or a heterogeneous colloid. Light passes through unobstructed Light passes through unobstructed –the mixture is a solution. Light passes, but the beam can be seen in the mixture Light passes, but the beam can be seen in the mixture –the mixture is a homogeneous colloid John Tyndall, Brittish, c1860

Back Bires, 2005 Slide 8Electrolytes Electrolytes Electrolytes –Solutions that conduct electricity. Ionic solutions are electrolytes. Ionic solutions are electrolytes. Covalent solutions are nonelectrolytes. Covalent solutions are nonelectrolytes. Is saltwater (NaCl in water) an electrolyte? Is saltwater (NaCl in water) an electrolyte? Is sugar water (C 6 H 12 O 6 in water) an electrolyte? Is sugar water (C 6 H 12 O 6 in water) an electrolyte? Conductivity tester Conductivity tester –can tell us if a solution is an electrolyte, and sometimes, how strong an electrolyte is.

Back Bires, 2005 Slide 9Solubility Solubility Solubility –The extent to which a solute will dissolve in a solvent. (how much solute will dissolve) High solubility High solubility –large amounts of solute will dissolve in a solvent Low solubility Low solubility –only small amounts of solute will dissolve Increasing temperature increases the solubility of solids in liquids Increasing temperature increases the solubility of solids in liquids Increasing temperature decreases the solubility of gasses in liquids! … Increasing temperature decreases the solubility of gasses in liquids! …

Back Bires, 2005 Slide 10 Solid-Liquid and Gas-Liquid solubility with temperature

Back Bires, 2005 Slide 11 Gasses in liquids In addition to cold temperatures, high pressures increase solubility of gasses in liquids. In addition to cold temperatures, high pressures increase solubility of gasses in liquids. Henry’s Law: Henry’s Law: –solubility of a gas in a liquid increases with increasing pressure of that gas above the liquid.

Back Bires, 2005 Slide 12 Like Dissolves Like! Some solvents are polar, like magnets, having partial negative and partial positive ends. (H 2 O) Some solvents are polar, like magnets, having partial negative and partial positive ends. (H 2 O) Other solvents are nonpolar, having no “+” “-” poles Other solvents are nonpolar, having no “+” “-” poles Polar solutes tend to dissolve well in polar solvents… Polar solutes tend to dissolve well in polar solvents… Nonpolar solutes tend to dissolve well into nonpolar solvents. Nonpolar solutes tend to dissolve well into nonpolar solvents. “Like dissolves like” “Like dissolves like” Water is very polar. Does it dissolve polar substances or non polar substance? Water is very polar. Does it dissolve polar substances or non polar substance?

Back Bires, 2005 Slide 13Saturation Saturated Solution Saturated Solution –solution has as much solute as it will allow (equal to solubility) Unsaturated Solution Unsaturated Solution –more solute can dissolve into solution (less than solubility) Supersaturated Solution Supersaturated Solution –too much solute in solution-some will fall out (more than solubility) We express the quantitative amount of solute in a solution with concentration … We express the quantitative amount of solute in a solution with concentration …

Back Bires, 2005 Slide 14 Concentration - Molarity Concentration Concentration –the quantitative amount of solute present in a solution Molarity (M) – moles/liter Molarity (M) – moles/liter –number of moles solute in liters of solution We can use the T-chart method to find moles of solute present. We can use the T-chart method to find moles of solute present.

Back Bires, 2005 Slide 15 Try these Molarity questions What is the concentration [in Molarity] when 3 moles of NaCl are dissolved in 2 Liters of water? What is the concentration [in Molarity] when 3 moles of NaCl are dissolved in 2 Liters of water? How much (in liters) of a 0.1 M solution do you need to get 2 moles of solute? How much (in liters) of a 0.1 M solution do you need to get 2 moles of solute? How many moles of NaOH are present in 300mL of a 1M solution? How many moles of NaOH are present in 300mL of a 1M solution? How many grams of HCl are found in 100mL of a 2M solution? How many grams of HCl are found in 100mL of a 2M solution? 1.5 M “molar” 20 L.3 moles 7.2 grams

Back Bires, 2005 Slide 16 Concentration - Molality Molality (m) – moles/kilogram – number of moles solute in kilogram of solvent. Molality (m) – moles/kilogram – number of moles solute in kilogram of solvent. molality is used less often, but is important when we discuss colligative properties molality is used less often, but is important when we discuss colligative properties Remember, where Molarity is “per liter solution”, molality is “per kilogram of solvent” Remember, where Molarity is “per liter solution”, molality is “per kilogram of solvent”

Back Bires, 2005 Slide 17 Try these molality questions What is the concentration in molality when 2 moles of NaCl are dissolved in 4kg of water? What is the concentration in molality when 2 moles of NaCl are dissolved in 4kg of water? How many moles of solute are present in 1 kg of a 3 m solution? How many moles of solute are present in 1 kg of a 3 m solution? What mass of water do you need to add to 4 moles of NaCl to make a 2 m solution? What mass of water do you need to add to 4 moles of NaCl to make a 2 m solution? What is the molality of a solution created by dissolving 3.5 moles methanol in 340g of CCl 4. What is the molality of a solution created by dissolving 3.5 moles methanol in 340g of CCl 4..5 m “molal” 3 moles 2 kilograms 10.3 m

Back Bires, 2005 Slide 18 Solution Preparation By solid dissolving: By solid dissolving: 1. calculate how many grams are needed to create our volume of our desired molarity solution 1. calculate how many grams are needed to create our volume of our desired molarity solution 2. weigh out that mass, and add it to a volumetric flask 2. weigh out that mass, and add it to a volumetric flask 3. add some water and allow to dissolve 3. add some water and allow to dissolve 4. add water to the desired volume 4. add water to the desired volume By dilution of a standard solution: By dilution of a standard solution: 1. use the relationship M 1 V 1 =M 2 V 2 1. use the relationship M 1 V 1 =M 2 V 2 2. calculate volume of standard molarity solution to use to get desired volume of desired molarity solution. 2. calculate volume of standard molarity solution to use to get desired volume of desired molarity solution. End of chapter 13

Back Bires, 2005 Slide 19 Begin C14: Colligative Properties “Colligative” means depends on amount. “Colligative” means depends on amount. A colligative property of a solution depends on the amount of solute dissolved in solution. A colligative property of a solution depends on the amount of solute dissolved in solution. Physical Properties of a solution change because solute particles act like impurities, getting in the way of solvent particles. Physical Properties of a solution change because solute particles act like impurities, getting in the way of solvent particles. We add impurities to lower freezing points, increase boiling points, or reduce vapor pressure. We add impurities to lower freezing points, increase boiling points, or reduce vapor pressure. Ethyl glycol is added to water in your car’s radiator to increase water’s boiling point. The more impurities, the greater the change

Back Bires, 2005 Slide 20 Osmosis and Osmotic Pressure Osmosis is the travel of a solvent from an area of low concentration (high purity) to high concentration (low purity). Osmosis is the travel of a solvent from an area of low concentration (high purity) to high concentration (low purity). Examples of osmosis: Examples of osmosis: –A Cucumber placed in a conc. NaCl solution (brine) loses water, shrivels up, and becomes a pickle. –Limp carrots and celery, placed in water, become firm because water enters via osmosis. From pure to impure 

Back Bires, 2005 Slide 21 Will it dissolve? (Solubility Rules) Not all ionic solids (salts) will dissolve. Not all ionic solids (salts) will dissolve. We use solubility rules to decide if the substance will dissolve. We use solubility rules to decide if the substance will dissolve. Salts containing… Salts containing… 1. Alkali metal cations(+) are soluble. 2. NH 4 +, NO 3 -, ClO 3 -, SO 4 2- are soluble. 3. Pb +, Ag +, Hg 2+ are insoluble. 4. CO 3 -, PO 4 3-, S 2- are insoluble. Which of the following salts are soluble? Which of the following salts are soluble? NaCl, HgCO 3, Ca(NO 3 ) 2, AgF, PbI 2, FeSO 4 NaCl, HgCO 3, Ca(NO 3 ) 2, AgF, PbI 2, FeSO 4 BaSO4, SrSO4, and PbSO4 are insoluble HUGE ON THE AP TEST!

Back Bires, 2005 Slide 22 Dissociation and Ions Present Dissociation = a salt dissolving into its ions: Dissociation = a salt dissolving into its ions: How many moles of ions are in a solution of 1 mole of NaCl? How many moles of ions are in a solution of 1 mole of NaCl? How many moles of ions are in solutions of 1 mole of each of the following?: How many moles of ions are in solutions of 1 mole of each of the following?:

Back Bires, 2005 Slide 23 Net Ionic Equations When we write a balanced chemical equation, we show all species present (all reactants and all products): When we write a balanced chemical equation, we show all species present (all reactants and all products): In a net ionic equation, we show only precipitates formed, and the reactants that form them: In a net ionic equation, we show only precipitates formed, and the reactants that form them: The chemicals that stay ions are called spectator ions, And are left out (Na +, NO 3 - ) The chemicals that stay ions are called spectator ions, And are left out (Na +, NO 3 - ) Remember to Balance HUGE ON THE AP TEST!

Back Bires, 2005 Slide 24 Net Ionic Equation Practice Write the net ionic equations for the following: Write the net ionic equations for the following:

Back Bires, 2005 Slide 25 Strong/Weak Electrolytes Recall that a solid compound made up of a cation and anion is called a salt. Recall that a solid compound made up of a cation and anion is called a salt. Salts that dissolve completely into their ions when put in water dissociate completely. Salts that dissolve completely into their ions when put in water dissociate completely. Salts that dissociate completely form strong electrolytes – solutions that conduct electricity well. Salts that dissociate completely form strong electrolytes – solutions that conduct electricity well. Some salts only partially dissociate, forming weak electrolytes – solutions that conduct electricity, but do so poorly. Some salts only partially dissociate, forming weak electrolytes – solutions that conduct electricity, but do so poorly.

Back Bires, 2005 Slide 26 H + / OH - Ions – (Acids and Bases) When a H + ion is released into solution, a H 3 O + ion is produced, called Hydronium ion. When a H + ion is released into solution, a H 3 O + ion is produced, called Hydronium ion. When a OH- ion is produced, we call this a Hydroxide ion. When a OH- ion is produced, we call this a Hydroxide ion. Hydronium (H 3 O + ) and Hydroxide (OH - ) are the fundamental ions involved in acid/base chem. Hydronium (H 3 O + ) and Hydroxide (OH - ) are the fundamental ions involved in acid/base chem. Acids that dissociate completely, releasing H+ ions form strong electrolytes. Acids that dissociate completely, releasing H+ ions form strong electrolytes. Bases that dissociate completely releasing OH- ions form strong electrolytes. Bases that dissociate completely releasing OH- ions form strong electrolytes. End of chapter 14 – Problem set on next slide

Back Bires, 2005 Slide 27 Chapter 14 Quiz Review Problems In your text, on page 447, do the following (for a grade) as a quiz review: In your text, on page 447, do the following (for a grade) as a quiz review: #1-2 : Solubility of salts #1-2 : Solubility of salts #13-15 : Dissociation of aqueous salts #13-15 : Dissociation of aqueous salts #16-18 : Precipitation reactions, net ionic equations, and spectator ions #16-18 : Precipitation reactions, net ionic equations, and spectator ions