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ACIDS AND BASES. Properties of Acids. Acids taste sour Acids effect indicators Blue litmus turns red Methyl orange turns red Acids have a pH lower than 7 Acids are proton (hydrogen ion, H + ) donors Acids react with active metals, produce H 2 Acids react with carbonates

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  2. Properties of Acids • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids have a pH lower than 7 • Acids are proton (hydrogen ion, H+) donors • Acids react with active metals, produce H2 • Acids react with carbonates • Acids neutralize bases

  3. Acids you must know: Strong Acids Weak Acids Sulfuric acid, H2SO4 Phosphoric acid, H3PO4 Hydrochloric acid, HCl Acetic acid, HC2H3O2 Nitric acid, HNO3

  4. Properties of Bases • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns purple • Bases have a pH greater than 7 • Bases are proton (hydrogen ion, H+) acceptors • Solutions of bases feel slippery • Bases neutralize acids

  5. Examples of Bases • Sodium hydroxide (lye), NaOH • Potassium hydroxide, KOH • Magnesium hydroxide, Mg(OH)2 • Calcium hydroxide (lime), Ca(OH)2

  6. Lewis acids Lewis Acid Bronsted-Lowry Bronsted-Lowry Definitions A Bronsted-Lowry acid is a proton donor; it donates a hydrogen ion, H+. A Bronsted-Lowry base is a proton acceptor; it accepts a hydrogen ion, H+. Lewis Definitions A Lewis acid is a substance than can accept (and share) an electron pair. A Lewis base is a substance than can donate (and share) an electron pair. Acid Definitions Arrhenius acids Arrhenius Acids and Bases Acids release hydrogen ions in water. Bases release hydroxide ions in water. An acid is a substance that produces hydronium ions, H3O+, when dissolved in water.

  7. Acid Definitions Lewis acids The Arrhenius model of acids and bases was broadened by the Bronsted-Lowry model. The Lewis acid-base model is the most general in scope. The Lewis definition of an acid includes any substance that is an electron pair acceptor; a Lewis base is any substance that can act as an electron pair donor. Bronsted-Lowry Arrhenius acids Ralph A. Burns, Fundamentals of Chemistry 1999, page 483

  8. Acid – Base Systems

  9. Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids H3PO4 HCl H2SO4 HC2H3O2 H2CO3 HNO3

  10. Ionization of HCl and formation of hydronium ion, H3O+ H2O + HCl  H3O+ + Cl- Proton acceptor Proton donor

  11. Self-Ionization of Water H2O + H2O  H3O+ + OH- Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

  12. Ion Concentration in Solutions

  13. Kw – Ionization Constant for Water In pure water at 25 C: [H3O+] = 1 x 10-7 mol/L [OH-] = 1 x 10-7 mol/L Kw is a constant at 25 C: Kw = [H3O+][OH-] Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14

  14. pH scale : measures acidity/basicity ACID BASE 10x 100x 10x 10x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NEUTRAL Each step on pH scale represents a factor of 10. pH 5 vs. pH 6(10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different)

  15. H+, OH-, and pH

  16. Calculating pH, pOH pH = -log10(H3O+) pOH = -log10(OH-) Relationship between pH and pOH pH + pOH = 14 Finding [H3O+], [OH-] from pH, pOH [H3O+] = 10-pH [OH-] = 10-pOH

  17. Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids

  18. Strong Acid Dissociation

  19. Weak Acid Dissociation

  20. Acids Effect Indicators Blue litmus paper turns red in contact with an acid.

  21. Acids Have a pH less than 7

  22. Effects of Acid Rain on Marble(calcium carbonate) George Washington: BEFORE George Washington: AFTER

  23. Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

  24. Bases have a pH greater than 7

  25. Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

  26. Acids Neutralize Bases HCl + NaOH  NaCl + H2O Neutralization reactions ALWAYS produce a salt and water.

  27. NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Neutralization Neutralization is a chemical reaction between an acid and a base to produce a salt (an ionic compound) and water. base acid salt water Some neutralization reactions: Na2SO4 + 2 HOH H2SO4(aq) + NaOH(aq) 2 sulfuric acid sodium hydroxide sodium sulfate water Ca(C2H3O2)2 + 2 HOH 2 HC2H3O2(aq) + Ca(OH)2(aq) acetic acid calcium hydroxide calcium acetate water

  28. Neutralization ACID+ BASE  SALT + WATER HCl + NaOH  NaCl + H2O strong strong neutral HC2H3O2 + NaOH  NaC2H3O2 + H2O weak strong basic • Salts can be neutral, acidic, or basic. • Neutralization does not mean pH = 7. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  29. NaCl(s) + H2O(l) Na1+(aq) + Cl1-(aq) Salts NaCl Salts - Ionic compounds containing a positive ion other than the hydrogen ion and a negative ion other than the hydroxide ion. i.e., a metal and a non-metal

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