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Chapter 13, (14): Mixtures and Aqueous Solutions

Chapter 13, (14): Mixtures and Aqueous Solutions. We use solutions all the time. What are they? Where do we find them? How do we describe them?. Soluble and Insoluble. Soluble means: able to be dissolved . Ionic solids (made of cation and anion) dissociate into their ions in water.

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Chapter 13, (14): Mixtures and Aqueous Solutions

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  1. Chapter 13, (14):Mixtures and Aqueous Solutions We use solutions all the time What are they? Where do we find them? How do we describe them?

  2. Soluble and Insoluble • Soluble means: able to be dissolved. • Ionic solids (made of cation and anion) dissociate into their ions in water. • Covalent solids (like sugar) dissolve when they are relatively polar. • The dissolved particles cannot be easily seen or separated from the solution. • “Like dissolves like” • Alloys are solutions of metals! • Solubility depends upon temperature…

  3. Increasing temperature increases the solubility of solids in liquidsIncreasing temperature decreases the solubility of gasses in liquids! …

  4. Gasses in liquids • In addition to cold temperatures, high pressures increase solubility of gasses in liquids. • Henry’s Law: • solubility of a gas in a liquid increases with increasing pressure of that gas above the liquid.

  5. Saturation • Saturated Solution • solution has as much solute as it will allow • Unsaturated Solution • more solute can dissolve into solution • Supersaturated Solution • too much solute in solution-some will come out • We express the quantitative amount of solute in a solution with concentration … (later)

  6. Parts of a solution • The dissolving medium is the solvent (what does the dissolving…the dissolver) • The dissolved substance is the solute (what gets dissolved…the dissolvey) • The solute andsolventtogether form the solution. • Solvents and solutes can be any phase. solution

  7. Special types of mixtures - 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. • Muddy water and Italian salad dressing are good examples of suspensions.

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

  9. The Tyndall Effect John Tyndall, Brittish, c1860 • The Tyndall effect allows us to distinguish between solutions, colloids, and suspensions. • It works by shining a beam of light into the mixture. If… • Light is blocked at entry into the mixture • the mixture is a suspension. • Light passes through unobstructed • the mixture is asolution. • Light passes, but the beam can be seen in the mixture • the mixture is a colloid.

  10. Electrolytes • Electrolytes • Solutions that conduct electricity. • Ionic solutions are electrolytes. • Covalent solutions are nonelectrolytes. • Is saltwater (NaCl in water) an electrolyte? • Is sugar water (C6H12O6 in water) an electrolyte? • Conductivity tester • can tell us if a solution is an electrolyte, and sometimes, how strong an electrolyte is.

  11. Concentration - Molarity • Concentration • the quantitative amount of solute present in a solution • 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.

  12. Try these Molarity exercises • What is the concentration [in Molarity] when 3.0 moles of NaCl are dissolved in 2.0 Liters of water? • How much (in liters) of a 0.10 M solution do you need to get 2.0 moles of solute? • How many moles of NaOH are present in 300.mL of a 1.0M solution? • How many grams of HCl are found in 100mL of a 2.0M solution? • What mass of NaOH is required to be dissolve in 250mL of water to make a 2.8M solution? 1.5 M“molar” 20 L .30 moles 7.3 grams 28 g NaOH

  13. Concentration - Molality • Molality (m) – moles/kilogram – number of moles solute in kilogram of solvent. • used less often, but important for colligative properties

  14. Try these molality exercises • 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 2 kg of a 3 m solution? • What mass of alcohol do you need to add to 4 moles of benzene to make a 2 m solution? • What is the molality of a solution created by dissolving 3.50 moles methanol in 340g of CCl4. • What mass of ethanol (C2H5OH) is required to add to 4.5 kg of water to create a .86 m solution? .5 m “molal” 6 moles 2 kilograms 10.3 m 180 g C2H5OH

  15. Solution Preparation • By solid dissolving: • 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 flask • 3. add some water and allow to dissolve • 4. add water to the desired volume • By dilution of a standard solution: • 1. use the relationship M1V1=M2V2 • 2. calculate volume of standard molarity solution to use to get desired volume of desired molarity solution. End of chapter 13…C14 (quant sol) next

  16. Begin C14: Colligative Properties • “Colligative” means depends on amount. • property of a solution depends on the amount of solute dissolved in solution. • Physical Properties of a solution change because solute particles act as impurities, getting in the way of solvent particles. • lowers freezing points • increases boiling points • reduces vapor pressure. The more impurities, the greater the change Ethyl glycol is added to water in your car’s radiator to increase water’s boiling point.

  17. Osmosis • travel of a solvent • from an area of low concentration to high concentration • From high purity to low purity. • 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

  18. Dissociation and Ions Present • 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 solutions of 1 mole of each of the following?:

  19. Strong/Weak Electrolytes Review • 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 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.

  20. H+ / OH-Ions – (Acids and Bases) • When a H+ ion is released into solution, a H3O+ ion is produced, called Hydronium ion. • When a OH- ion is produced, we call this a Hydroxide ion. • Acids that dissociate completely, releasing H+ ions form strong electrolytes. • Bases that dissociate completely releasing OH- ions form strong electrolytes. End of chapter 13,(14) – Problem set on next slide

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