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Understanding Acid-Base Chemistry: Properties and Equilibrium Reactions

Explore the fundamental concepts of acids and bases, Brønsted-Lowry theory, equilibrium reactions, pH scale, strong and weak acids, bases, polyprotic acids, and salt solutions. Learn how to determine solution acidity and basicity based on concentrations of hydronium and hydroxide ions.

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Understanding Acid-Base Chemistry: Properties and Equilibrium Reactions

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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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