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CHAPTER 14

CHAPTER 14. AP CHEMISTRY. NATURE OF ACIDS AND BASES. Acids - sour Bases (alkali) - bitter and slippery Brønsted-Lowry Acid is a proton [H + ] donor, base is a proton acceptor H + never found in water, will always form the hydronium ion

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CHAPTER 14

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  1. CHAPTER 14 AP CHEMISTRY

  2. NATURE OF ACIDS AND BASES • Acids - sour • Bases (alkali) - bitter and slippery • Brønsted-Lowry • Acid is a proton [H+] donor, base is a proton acceptor • H+ never found in water, will always form the hydronium ion • HA(aq) + H2O(l) --> H3O+(aq) + A-(aq) Acid Base Conj. Acid Conj. Base • ka = [H+][A-] [HA] • Diprotic acid - forms two protons • Page 627 table 14.1

  3. Continue • Carboxyl group • Page 628 table 14.2 • Arrange the following species to strength as a base H2O, F-, CN-, Cl-, NO2-

  4. WATER AS AN ACID OR BASE • Amphoteric - can be either an acid or base • OH- — H2O — H3O+ • NH2- — NH3 — NH4+ • Any aqueous solution that contains H3O+ ions and OH- ions will eventually reach equilibrium • 2 H2O <==> H3O+(aq) + OH-(aq)

  5. Continue • Any pure solids or liquids do not have concentrations, therefore they are not placed in the equation • kw = [ H3O+][OH-] = 1.0 X 10-14 at 25 °C • When [ H3O+] = [OH-] = 1.0 X 10-7 a reaction will be neutral • [ H3O+] < [OH-] the solution is basic • [ H3O+] > [OH-] the solution is acidic • Calculate the [H3O+] or [OH-] opposite of what you have and state if the solution is neutral, acidic, or basic • 2.0 X 10-5 M H3O+ • 3.0 X 10-9 M OH- • 1.0 X 10-7 M OH- • Orange juice demo

  6. pH SCALE • pH = -log [H+] • Significant figures of the concentration is equal to the number of places after the decimal point. • 1.0 X 10-9 two sig. figs. so the pH will have two decimal places pH = 9.00 • pOH = -log[OH-] • pk = -log k • [H+] = 10-pH • pH = 7 neutral, pH < 7 acidic, pH > 7 basic

  7. STRONG ACIDS • HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3 • Look for the major components found in the solution • HCl(aq) has H+, Cl-, and H2O • Look at what can give H+ • H2O <=> H+ + OH- • HCl ---> H+ + Cl- • Water gives such a small amount of hydrogen ions we can ignore it

  8. WEAK ACID • HF(aq) species are H+, F-, H2O. Look at those which can give H+ • HF(aq) <=> H+ (aq) + F-(aq) ka = 7.2 X 10-4 • H2O(aq) <=> H+(aq) + OH-(aq) ka = 1 X 10-14 • HF is a weak acid but it is stronger than water so it is the dominant source of H+ • HX(aq) + H2O(l) <=> H3O+(aq) + X-(aq)

  9. Continue • Go over example page 639 • % dissociation = amount dissociated X 100 • Initial concentration • Page 641 example • STRONG BASES - group 1 metals, calcium, barium, and strontium

  10. AMINE GROUPS • B(aq) + H2O(l) <=> BH+(aq) + OH-(aq) • kb= [BH+][OH-] [B] • Page 647 table 14.3 • Page 647-650 example • ka X kb = kw

  11. POLYPROPTIC ACID • Can furnish more than one proton • H3PO4 <=> H+ + H2PO4- ka = 7.5 X 10-3 • H2PO4- <=>H+ + HPO42- ka = 6.2 X 10-8 • HPO42- <=> H+ + PO43- ka = 4.8 X 10-13 • With each proton lost the ka becomes smaller • Page 651 table 14.4 • Page 651 example • metallic oxides are strong bases • O2- + H2O <=> 2OH-

  12. ACID-BASE PROPERTIES OF SALT SOLUTIONS • Cations • Spectators - derived from a strong base • Li+, Na+, K+, Ca2+, Sr2+, Ba2+ • Acidic - all other cations (transition metals included) • Anions • Spectators - derived from a strong acid • Cl-, Br-, I-, NO3-, ClO4-, SO42- • Basic - derived from a weak acid • F-, NO2-, CO32- • If the cation is acidic and anion basic, you look at their ka and kb

  13. ACID-BASE CHARACTERS • Any molecule with a H-X bond can be an acid IF TWO rules are followed • In general metal hydrides are basic or have no acid-base properties • Nonmetal hydrides are acidic or have no acid- base properties • Pages 659-661 examples and tables 14.5, 14.6, 14.7 • Read 662-669

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