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Chapter 15

Chapter 15. Acids and Bases. Objectives. Describe the properties of acids and bases Recognize acids and bases by definitions Compare strong and weak acids/bases Describe electrolytes. What Do You Know About Acids and Bases?. Properties of Acids. Sour taste

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Chapter 15

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  1. Chapter 15 Acids and Bases

  2. Objectives • Describe the properties of acids and bases • Recognize acids and bases by definitions • Compare strong and weak acids/bases • Describe electrolytes

  3. What Do You Know About Acids and Bases?

  4. Properties of Acids • Sour taste • (A VERY bad way to test in the lab!) • What acids have you tasted? • Turns blue litmus red • Reacts with metal to form hydrogen gas • pH less than 7 • Electrolyte • Solutions that conduct electrical current

  5. Properties of Bases • Tastes bitter • (Also not a good lab practice!) • Turns red litmus blue • pH greater than 7 • Electrolyte

  6. Acid/Base Definitions • Arrhenius Definition • Acids increase the H+ ion concentration in solution • Acids have H as the first element • Bases increase the OH- ion concentration in solution • Many bases end with OH • Definition limited to solutions!

  7. Acid/Base Definitions • Bronsted/Lowry Definition • Acids are H+ donors • H+ ion is just a proton • (often called proton donors) • Bases are H+ acceptors • (Often called proton acceptors) • This is the definition of acids and bases we will use the most.

  8. Strong Acids • Strong Acids – Acids that completely ionize in solution • Assume that HA can be an acid HA  H+ + A- • There will be NO HA left in solution • Strong Acids – Memorize the first 3 HNO3 HCl H2SO4 HClO4 HBr HI

  9. The Hydronium Ion • H+ ions can be written one of two ways • 1st H+ • Easy way to indicate the ion • 2nd H3O+ • Indicates that the H+ attaches to water molecules • Hydronium Ion • Either way is fine

  10. Weak Acids • Weak Acids – Acids that only partially ionize in solution • Equilibrium is established • Assume HA to be a weak acid HA + H2O  H3O+ + A- • There will be lots of HA left in solution • Weak Acids – Any acid that is not strong H2CO3 HF H3PO4 HNO2 HC2H3O2 H2SO3

  11. Inorganic vs Organic Acids • All acids have H in the formula • Inorganic acids contain hydrogen and a halogen or hydrogen and a polyatomic ion • Organic acids have hydrogen and carbon and oxygen (not CO3-2) • Carboxyl group • Carboxylic acids • All weak

  12. Strong Bases • Strong Bases – Bases that completely ionize in solution KOH  K+ + OH- • There will be NO KOH left in solution • Strong Bases NaOHKOH • Group 2 hydroxides are also considered strong bases

  13. Weak Bases • Weak Bases – Bases that partially ionize in solution NH3 + H2O  NH4+ + OH- • There will be lots of NH3 left in solution • Weak bases are ammonia derivates • They will have nitrogen in them

  14. Electrolytes • Conduct current because charged particles are free to move about • Acids form ions when they are dissolved in solution HCl  H+ + Cl- • Salts form ions when they are dissolved in solution NaNO3  Na+ + NO3- • Charged particles complete (or close) the circuit

  15. Closed Circuit

  16. Open Circuit

  17. Another Type of Open Circuit

  18. Closed circuit • Ions in solution close the circuit • Charges flow to the opposite pole • Current flows from negative to positive • Light bulb shines!

  19. Nonelectrolytes • Solutions that do not conduct an electric current • No ions are present • Nothing to conduct the current • All molecules are nonelectrolytes • They dissolve into individual molecules

  20. Electrolytes or Nonelectrolytes? • CH4 • Nonelectrolyte • KBr • Electrolyte • C2H6O • Nonelectrolyte • H2SO4 • Electrolyte

  21. Strong and Weak Electrolytes • Strong electrolytes • Solutions that conduct current well • Lots of ions in solution • Strong acids and bases, salts • Weak electrolytes • Solutions that conduct current poorly • Few ions • Weak acids and bases

  22. Homework • p. 625 #42,43,51,55,61,67,70,86,97

  23. Objectives • Recognize polyprotic acids. • Compare the strengths of weak acids and bases. • Describe a neutralization reaction • Calculate neutralization data • Determine if a solution is acidic, basic, or neutral • Explain the autodissociation of water

  24. Polyprotic Acids • Acids that can donate more than 1 hydrogen • H2CO3 – Carbonic Acid • Able to donate 2 H’s • Diprotic • H3PO4 – Phosphoric Acid • Able to donate 3 H’s • Triprotic

  25. Cont. • HNO3 – Nitric Acid • Only 1 H to donate • Monoprotic • HC2H3O2 – Acetic Acid • Only the first H can be donated • Same with most carboxylic acids

  26. How Weak is Weak?Quantifying Weak Acids and Bases • Weak acids and bases have equilibrium dissociation values • The smaller the constant the weaker the acid or base • The larger the constant the stronger the acid or base

  27. How Weak is Weak?Quantifying Weak Acids and Bases Acid - HA(aq) H+ + A- • The Equilibrium Expression Ka = [H+] [A-] / [HA] Base - B(aq) + H2O  BH+ + OH- • The Equilibrium Expression Kb = [BH+] [OH-] / [B]

  28. Sample Ka Values • Acid Ka • HClO2 1.2x10-2 • HF 7.2x10-4 • HC2H3O2 1.8x10-5 • HClO 3.5x10-8 • HCN 6.2x10-10 • HIO 2.0x10-11 • What is the strongest / weakest acid?

  29. Sample Kb Values • Base Kb • NH3 1.8x10-5 • (C2H5)2NH 1.3x10-3 • (C2H5)3N 4.0x10-4 • CH3NH2 4.4x10-4 • C2H5NH2 5.6x10-4 • What is the strongest / weakest base?

  30. Neutralization Reactions • The reaction of an acid and a base to yield a salt and water • HI + KOH  HOH + KI • Net Ionic Equation • Net Ionic is ALWAYS the same

  31. Example • What volume of 0.25M KOH is required to react with 50.0 mL of 0.20 M HBr?

  32. Example • What volume of 1.2M NaOH is required to react with 30.0 mL of 0.70 M H2SO4?

  33. Acidic, Basic, and Neutral Solutions • Relates to concentrations of H+ and OH- • Acidic solutions have more H+ than OH- • H+ from an acid • Basic solutions have more OH- than H+ • OH- from base • Neutral solutions have equal amounts of both ions • Both ions come from water!

  34. Autoionization of Water • Water molecules dissociate by themselves H2O(l) H+ + OH- • In pure water the concentrations are equal • Both 1.00x10-7M • Write the equilibrium expression • Kw is always 1.00x10-14 at 25ºC

  35. LeChatlier’s Principle (Again) • The concentration of H+ and OH- can vary in solution. • When H+ is added, [OH-] decreases • When OH- is added, [H+] decreases • That is how solutions become acidic or basic

  36. Example • What is the concentration of H+ and OH- in a 0.10M solution of HCl? Is the solution acidic, basic, or neutral?

  37. Example • A solution is prepared by dissolving 6.00 grams of KOH in 200.0mL of water. What is the concentration of H+ and OH-? Is the solution acidic, basic, or neutral?

  38. Homework • p. 626 #80,87,89,92,101,117,119,124,131,134

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