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SOLUTIONS 19.2

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  1. SOLUTIONS 19.2

  2. Chapter Nineteen: Solutions • 19.1 Water • 19.2 Solutions • 19.3 Acids, Bases, and pH

  3. Chapter 19.2 Learning Goals • Explain how solutions are formed. • Define solubility and interpret solubility graphs. • Describe factors that affect the concentration of solutions. • Compare and contrast solubility of solid, liquid, and gaseous matter.

  4. 19.2 Water and solutions • A solution is a mixture of two or more substances that is uniform at the molecular level.

  5. 19.2 Water as a mixture • Muddy water not a solution. • Muddy water is heterogeneousbecause it contains larger particles of soil or plant debris.

  6. 19.2 Water and solutions • Although we often think of solutions as mixtures of solids in liquids, solutions exist in every phase; solid, liquid, or gas. • Solutions of two or more solids are called alloys. • Steel is an alloy (solution) of iron and carbon.

  7. 19.2 Suspensions • In a mixture called a suspension the particles can range widely in size. • Muddy water, a suspension, will settle when it is left still for a period of time.

  8. 19.2 Colloids • Colloids are mixtures, and look like solutions, but their particles are too small to settle to the bottom of their container over time. • Examples of colloids are mayonnaise, egg whites, and gelatin.

  9. 19.2 Tyndall effect • Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam.

  10. 19.2 Types of mixtures • How can you tell the difference between a solution, a colloid and a suspension? First, try filtering it, then look for the Tyndall effect.

  11. 19.2 Water and solutions • A solution contains at least two components: a solvent, and a solute. • The solvent is the part of a mixture that is present in the greatest amount. Which of these is the solvent?

  12. 19.2 Water and solutions • When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

  13. 19.2 Solubility • The term solubility means the amount of solute (if any) that can be dissolved in a volume of solvent. Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

  14. 19.2 Solubility • Chalk and talc do not have solubility values. • These substances are insoluble in water because they do not dissolve in water.

  15. 19.2 Solubility • A solution is saturated if it contains as much solute as the solvent can dissolve. • Any solute added in excess of the substance’s solubility will not dissolve. What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

  16. Solving Problems Seawater is a solution of water, salt, and other minerals. How much salt can dissolve in 200 mL of water at 25 °C? • Looking for: • …grams of solute • Given • … v = 200 mL; T = 25 C

  17. Solving Problems • Looking for: • …grams of solute • Given • … v = 200 mL water; T = 25 C • Relationships: • Solubility table for reference • 38 g of salts in 100 mL water at 25 °C • Solution • …if there are 38 g salt/100 mL water, then • “x” g/ 200 mL water • = 76 g salts are need in 200 mL of water

  18. 19.2 Solubility • A solution is saturated if it contains as much solute as the solvent can hold. • An examples of a saturated solution is air. • Air can be saturated with water. (We call it humidity!)

  19. 19.2 Solubility • For something to dissolve in water, the water molecules need to break the bonds between the solute molecules. • Water dissolves each substance differently because the chemical bond strengths between atoms found in different solutes are not the same.

  20. 19.2 Solubility graphs • Solubility values for three solutes are plotted in this temperature-solubility graph.

  21. 19.2 Concentration • In chemistry, it is important to know the exact concentration of a solution—that is the exact amount of solute dissolved in a given amount of solvent.

  22. 19.2 Concentration • Two other common ways of expressing the concentration of a solution are molarity and mass percent.

  23. 19.2 Concentration • Molarityis equal to the moles of solute per liter of solution.

  24. 19.2 Concentration • The mass percent of a solution is equal to the mass of the solute divided by the total mass of the solution multiplied by 100%.

  25. Solving Problems • How many grams of salt (NaCl) do you need to make 500 grams of a solution with a mass percent of 5% salt? The formula mass of NaCl is 58.4 g/mol. • What is the molarity of this solution? • Looking for: • …grams of solute • Given • … mass solvent = 500 g; concentration = 5% • …formula mass = 58.4 g/mol

  26. Solving Problems • Relationships: • Mass percent = mass of solute x 100% total mass of solution • Molarity = moles of solution liter of solution • Solution • …5% = (mass of salt ÷ 500 g) × 100% • …0.05 × 500 g = 25 g • # of moles = 25 g = .4 moles 58.4 g/mol • Assume 1 L of solution = .4 moles/L = .4M

  27. 19.2 Equilibrium • When a solute like sugar is mixed with a solvent like water, two processes are actually going on continuously. • Molecules of solute dissolve and go into solution. • Molecules of solute come out of solution and become “un-dissolved.” • When the rate of dissolving equals the rate of coming out of solution, we say equilibriumhas been reached.

  28. 19.2 Equilibrium • When a solute like sugar is mixed with a solvent like water, two processes are actually going on continuously. • Molecules of solute dissolve and go into solution. • Molecules of solute come out of solution and become “un-dissolved.” • When the rate of dissolving equals the rate of coming out of solution, we say equilibriumhas been reached.

  29. 19.2 Equilibrium • When a solution is unsaturated its concentration is lower than the maximum solubility. • A supersaturated solution means there is more dissolved solute than the maximum solubility.

  30. 19.2 Solubility of gases in liquids • Some solutions have a gas as the solute. • When you drink carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

  31. 19.2 Solubility of gases in liquids • When temperature increases, the solubility of gases in liquid decreases.

  32. 19.2 Solubility of gases in liquids • The variety and no. or organisms is controlled somewhat by the relationship between dissolved oxygen and temperature.

  33. 19.2 Solubility of gases in liquids • Oil and vinegar salad dressing separates because oil is not soluble in water. • Liquids that are not soluble in water may be soluble in other solvents.

  34. 19.2 Solubility rules • A set of solubility rules helps predict when an ionic compound is soluble or insoluble.

  35. Key Question: How is the solubility of a gas affected by temperature? Investigation 19C Solubility of CO2