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

3. 19.2 Water and solutions  A solution is a mixture of two or more substances that is uniform at the molecular level.

4. 19.2 Water as a mixture  Muddy water not a solution.  Muddy water is heterogeneous because it contains larger particles of soil or plant debris.

5. 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.

6. 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.

7. 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.

8. 19.2 Tyndall effect  Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam.

9. 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.

10. 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?

11. 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? 1.Looking for:  …grams of solute 2.Given  … v = 200 mL; T = 25  C

17. 1.Looking for:  …grams of solute 2.Given  … v = 200 mL water; T = 25  C 3.Relationships:  Solubility table for reference  37.7 g of salts in 100 mL water at 25 °C 4.Solution  …if there are 37.7 g salt/100 mL water, then  “x” g/ 200 mL water  = 75.4 g salts are need in 200 mL of water Solving Problems

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 graphs  Solubility values for three solutes are plotted in this temperature-solubility graph.

20. 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.

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  Molarity is 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? 1.Looking for:  …grams of solute 2.Given  … mass solvent = 500 g; concentration = 5%  …formula mass = 58.4 g/mol

26. 3.Relationships:  Mass percent = mass of solute x 100% total mass of solution  Molarity = moles of solution liter of solution 4.Solution  … 5% = (mass of salt ÷ 500 g) × 100%  …0.05 × 500 g = 25 g  # of moles = 25 g =.4 moles 58.4 g/mol  Molarity =.4 mol/.5 L =.8 M solution Solving Problems

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 equilibrium has 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 equilibrium has 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.

31. 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 (CO 2 ).

32. 19.2 Solubility of gases in liquids  When temperature increases, the solubility of gases in liquid decreases.

33. 19.2 Solubility of gases in liquids  The variety and no. or organisms is controlled somewhat by the relationship between dissolved oxygen and temperature.

34. 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.