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Lesson 12 Acids, Bases, and Salts

Lesson 12 Acids, Bases, and Salts. Anything in black letters = write it in your notes (‘knowts’). 12.1 – Definitions. Acids. Taste sour. Dissolve active metals to produce hydrogen gas. Turns litmus paper RED. Bases. Taste bitter. Feels slippery on skin (dissolves oils on skin).

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Lesson 12 Acids, Bases, and Salts

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  1. Lesson 12 Acids, Bases, and Salts Anything in black letters = write it in your notes (‘knowts’)

  2. 12.1 – Definitions Acids Taste sour Dissolve active metals to produce hydrogen gas Turns litmus paper RED Bases Taste bitter Feels slippery on skin (dissolves oils on skin) Turns litmus paper BLUE Have you seen the litmus paper yet?? These are experimental definitions, they do not explain (theory) how an acid is different from a base.

  3. Arrhenius defined an acid and base theoretically. Svante Arrhenius (1857 – 1927)

  4. Dissociate - to split or separate from another

  5. Arrhenius Definition (~1887) ACID – substance that dissociates in water to form hydrogen ions (H+). HCl (aq) H+ (aq) + Cl- (aq) BASE – substance that dissociates in water to form hydroxide ions (OH-). NaOH (aq) Na+ (aq) + OH- (aq)

  6. When an acid is placed in water, H+ ions are produced.

  7. Acid/Base Indicators Litmus Acid – red, Base – blue, Neutral - colorless Phenolphthalein Acid – colorless, Base – pink, Neutral - colorless Cabbage Acid – red/pink, Base – yellow/green, Neutral – blue/purple

  8. 12.2 – pH Scale Molarity (M) – unit used to express the concentration of a solution mol solute (mol) Molarity = liters of soln (L) anything in [brackets] means the concentration in molarity [H+] = ‘the hydrogen ion concentration’ [OH-] = ‘the hydroxide ion concentration’

  9. Self-Ionization of Water Water ionizes to produce a small amount of H+ and OH- ions. H2O H+ + OH-

  10. H2O H+ + OH- In pure water at 25̊C [H+] = [OH-] = 1 x 10-7 M

  11. remember…anything in [brackets] represents the concentration in molarity A solution is acidic if [H+] > 1.0 x 10-7 M …or if the pH of the solution is below 7

  12. Just as the mole was used to simplify large numbers of atoms, pH is used to simplify small concentration numbers pH = ‘power of the hydrogen ion’ pH = -log[H+] Instead of writing out numbers like these… pH = 7.00 [H+] = 1 x 10-7 M [H+] = 2.4 x 10-4 M pH = 3.62 [H+] = 7.3 x 10-10 M pH = 9.14 we can write number like these

  13. Instead of saying “This solution has a hydronium ion concentration of 2.4 x 10-4 M”. We can just say “This solution has a pH of 3.62”. Not only is pH an easier number to talk about, pH is understood by most people, whereas molarity is not. The pH scale is used to describe how acidic or basic (alkaline) a substance is.

  14. Examples Pure water has [H+] = 1.00 x 10-7 M The pH of water would be pH = -log[H+] pH = - log [1.00 x 10-7] pH = 7

  15. Examples [H+] = 2.3 x 10-5 M. Calculate the pH. pH = - log [H+] pH = - log [2.3 x 10-5] pH = 4.64

  16. Examples [H+] = 1.0 x 10-5 M. Calculate the pH. pH = - log [H+] pH = - log [1.0 x 10-5] pH = 5.0

  17. Examples pH = 4.2. Calculate [H+] pH = - log [H+] -4.2 = log [H+] 10-4.2 = 10log [H+] 10-4.2 = 6.31 x 10-5 M = [H+]

  18. Summary of pH AcidicNeutralBasic [H+] 100 M 10-7 M10-14 M pH 0 7 14 [OH-] 10-14 M10-7 M 100 M pH = - log [H+] [H+] = 10-pH Kw = [H+][OH-] = 1.0 x 10-14

  19. 12.3 – Strengths of Acids and Bases Strong acids & bases completely dissociate (split into ions) in water; Weak acids & bases partly dissociate and only form a small amount of ions.

  20. HCl is a strong acid, HCl (aq) H+ (aq) + Cl- (aq) it completely ionizes

  21. CH3COOH is a weak acid, CH3COOH (aq)CH3COO- (aq) + H+ (aq) it forms a small amount of ions

  22. Other strong acids H2SO4 – sulfuric acid, HNO3 – nitric acid Strong bases NaOH – sodium hydroxide KOH – potassium hydroxide LiOH – lithium hydroxide

  23. Universal pH Indicator Color Chart

  24. 12.4 – Neutralization Reactions Neutralization Rxn – complete rxn of a strong base with a strong acid A neutralization rxn will produce a salt and water. Acid + Base  Salt + H2O HCl + NaOH  NaCl + H2O

  25. Titration – method used to determine the concentration of an unknown solution using a solution whose concentration is known. Standard – solution that has a known concentration. End Point – point where the indicator changes color

  26. EXAMPLE 10.0 mL of 0.5 M HCl solution is added to 20.0 mL of NaOH of unknown concentration. What is the concentration of the NaOH? HCl + NaOH  NaCl + H2O x M 0.5 M 10.0 mL 20.0 mL Since the reaction of HCl and NaOH is 1:1 and twice the volume of NaOH was used, the NaOH must half as strong as HCl; [0.25 M].

  27. EXAMPLE What volume of 0.10 M KOH is required to neutralize 20.0 mL of 0.20 M H2SO4 solution? H2SO4 + 2KOH  K2SO4 + 2H2O 0.20 M 0.10 M 20.0 mL x mL Since KOH requires twice as many moles as H2SO4, you should double your answer.

  28. 3. Write the neutralization reaction for the following reactants • a. Sodium hydroxide with hydrochloric acid • b. Lithium hydroxide with nitric acid • c. Calcium hydroxide with hydrochloric acid

  29. 3. Write the neutralization reaction for the following reactants • d. Sulfuric acid with potassium hydroxide • e. Phosphoric acid with sodium hydroxide • f. Sulfuric acid with calcium hydroxide

  30. Write the balanced chemical equation for each neutralization reaction Sulfuric acid + magnesium hydroxide Phosphoric acid + calcium hydroxide Nitric acid + ammonium hydroxide

  31. 1. What color will litmus paper be in an acidic solution? 2. What color will phenolphthalein indicator be in an basic solution? 3. What does [H+] mean? 4. What two products are always formed in an acid-base neutralization reaction?

  32. 5. Explain the difference between a strong acid and a weak acid. 6. Explain why the pH of pure water is 7.00 7. What is a buffer? 8. How is the molarity of a solution calculated?

  33. 9. A student titrated 10.0 mL of an HCl solution. The titration required 23.3 mL of 0.24M NaOH solution. • Which solution was the standard? • Which solution was more concentrated? • Calculate the molarity of the HCl solution.

  34. 10. Calculate the pH of solutions with the following hydrogen ion concentrations. a. [H+] = 1.23 x 10-4M b. [H+] = 3.42 x 10-7M 11. Calculate the hydrogen ion concentrations of solutions with the given pH. a. pH = 3.14 b. pH = 9.2

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