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Chapter 15

A.P. Chemistry. Chapter 15. Acids and Bases. General Stuff. Taste Litmus test. General Stuff. Phenolphthalein test Ppth with OH - Remember how to titrate?. General Stuff. pH scale based on an equilibrium system H 2 O <===> H + + OH - K w = 1x10 -14 at 25°C

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Chapter 15

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  1. A.P. Chemistry Chapter 15 Acids and Bases

  2. General Stuff • Taste • Litmus test

  3. General Stuff • Phenolphthalein test • Ppth with OH- • Remember how to titrate?

  4. General Stuff • pH scale • based on an equilibrium system • H2O <===> H+ + OH- • Kw = 1x10-14 at 25°C • pH scale is temperature dependent

  5. Acid Base Concepts H2O <===> H+ + OH- H2O + H2O <===> H3O+ + OH- • H+ and H3O+ are synonymous.

  6. Acid Base Definitions • Arrhenius: • Acids contain hydrogen and make H+ or (H3O+) in solution. • Bases contain hydroxide ions and make OH- in solution.

  7. Acid Base Definitions • Strong Acids are Arrhenius acids Substances that ions in solution are electrolytic

  8. Arrhenius Acids • HBr ----> H+ + Br- • HCl ----> H+ + Cl- • HI ----> H+ + I- • H2SO4 ----> 2H+ + SO4 2- • HClO4 ----> H+ + ClO4- • HNO3 ----> H+ + NO3-

  9. Acid Base Definitions • Strong bases are Arrhenius bases. Ammonia is a weak base.

  10. Arrhenius Bases • LiOH ------> Li+ + OH- • NaOH ------> Na+ + OH- • KOH ------> K+ + OH- • Ca(OH)2 ------> Ca2+ + 2OH- • Sr(OH)2 ------> Sr2+ + 2OH- • Ba(OH)2 ------> Ba2+ + 2OH-

  11. Acid Base Definitions • Bronsted-Lowry: • Acids are proton (H+) donors. • Bases are proton acceptors. Johannes Bronsted, Danish Chemist

  12. Acid Base Definitions • Bronsted Lowry acids and bases exist as conjugate pairs.

  13. Bronsted Lowry Examples • water + acetate ion • H2O + C2H3O2- <--->OH- + HC2H3O2 • hydrochloric acid + ammonia • HCl + NH3 <-----> NH4+ + Cl- • bicarbonate + hydrofluoric acid • HCO3- + HF <-----> H2CO3 + F-

  14. LEWIS Acids and Bases • Acids are electron pair acceptors • SO3, BF3, Al3+, CO2 Gilbert Newton Lewis

  15. LEWIS Acids and Bases • Bases: electron pair donors • NH3, O2-, H2O

  16. Traditional Examples • ammonia + boron trifluoride • NH3 + BF3 -----> H3NBF3 • Aluminum chloride + ammonia • AlCl3 + NH3 -----> Cl3AlNH3 • phosphorus trihydride and Boron trifluoride • PH3 + BF3 -----> H3PBF3

  17. LEWIS Acids and Bases • Complex ion formation is a Lewis acid Base reaction Colorful complex ions in ammonia

  18. Lewis Acids / “Complexers” • Remember the common “complexers” • Fe3+ Cu2+ Al3+ Co2+ Zn2+ Ag+

  19. Lewis Bases / “Complexers” • Ligands (bases) • CN- H2O OH- NH3 Cl- SCN- • recall the famous equilibrium complex: FeSCN2+

  20. More Lewis Acid Base (complex) examples • Aluminum nitrate solution and water • Al3+ + 6H2O -----> Al(H2O)63+ • Zinc acetate in excess sodium hydroxide solution • Zn2+ + 4OH- -----> Zn(OH)42-

  21. Lewis Acid Base (complex) examples • silver nitrate solution and concentrated ammonia solution • Ag+ + 2NH3 ----> Ag(NH3)2+ • copper II sulfate solution and excess ammonia • Cu2+ + 4NH3 -----> Cu(NH3)42+

  22. Lewis Acid Base (complex) examples • sodium cyanide solution and ferric nitrate • 6CN- + Fe3+ -----> Fe(CN)63-

  23. Complexes of centers with water • 2+ and 3+ centers • Al. Cu, Co, Fe, Zn • Complex with water • Examples…

  24. Acid Base species

  25. The Strong • perchloric, sulfuric, hydroiodic, hydrobromic, hydrochloric, nitric. • Strong bases…LI, Na, K, Ca, Sr, Ba hydroxides

  26. The Weak • Weak molecular acids: HCN, HF, HC2H3O2, H2SO3 and more. • Weak molecular bases: hydroxides of Mg, Cu, …. NH3, NH2CONH2 and more.

  27. The IONS • Acetate • Fluoride • Carbonate • Sulfite • Aluminum • Copper • Iron • Ammonium

  28. Amphiprotic • can act as either an acid or a base. • Depends on their environment.

  29. Why weak or strong? BONDING!

  30. Why weak or strong? Some ions attract H+ or OH- more than water does!

  31. HYDROLYSIS • To “split” water, react with water. • Why does it occur….

  32. Ground “rules” of hydrolysis • Anions of weak acids are basic in water. • Cations of weak bases are acidic in water. • Ions of strong acids and bases are neutral

  33. Hydrolysis Examples • magnesium iodide (a salt) • THINK: what acid and base would its ions make? • Mg2+ is from a weak base (acidic) • I- is from a strong acid (neutral) • MgI2 in water is acidic. • Mg2+ + 2H2O ----> Mg(OH)2(aq) +2 H+ • pH will be <7

  34. HYDROLYSIS • copper II bromide • THINK: what acid and base would its ions make? • Cu2+ is from a weak base and is acidic. • Br- is from a strong acid and is neutral. • CuBr2 in solution is acidic • Cu(H2O)42+ ----> Cu(H2O)3 (OH) 1+ (aq) + H+ • pH will be <7

  35. HYDROLYSIS • sodium sulfate • Neutral

  36. Hydrolysis Examples • strontium sulfite • base

  37. HYDROLYSIS • potassium acetate • BASIC! • iron III nitrate • ACIDIC!

  38. Hydrolysis Examples • sodium chloride • NEUTRAL! • cobalt nitrate • ACIDIC!

  39. HYDROLYSIS • aluminum sulfate • ACIDIC! • potassium carbonate • BASIC!

  40. How about NH4F?

  41. REMEMBER! • The “salt” of a weak base is acidic. • The “salt” of a weak acid is basic.

  42. Hydrolysis Lab…..Tuesday

  43. Acid Base Equilibria • In a reaction between acids and bases, equilibrium will favor the dissociation of the stronger acid.

  44. Weak and Strong Acids and Bases • RELATIVE STRENGTH OF Acids and Bases • See chart

  45. HC2H3O2 +H2O <===> C2H3O2-+H3O+ • Since hydronium ion is a stronger acid than acetic acid, the reactant side is favored here. Keq is small.

  46. Reason for varying acid base strength • bond strengths between ions • Strong acids and bases have WEAK bonds.

  47. Patterns • The weakest acids have the strongest conjugate bases. • The strongest acids have the weakest conjugate bases.

  48. Patterns • The weakest bases have the strongest conjugate acids. • The strongest bases have the weakest conjugate acids.

  49. Patterns • Determining factor is the bonding! • H+ acceptors vs. H+ donors

  50. Patterns • Weakest to strongest: • HCl, HBr, HI • Why? • SIZE!

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