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To understand two models of acids and bases

Learning Goals. To understand two models of acids and bases To understand how acids and bases ionize/dissociate in water. Basic (alkaline) solutions have bitter taste and are slippery. Ex.: soaps, “draino,” many household cleaning products.

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To understand two models of acids and bases

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  1. Learning Goals • To understand two models of acids and bases • To understand how acids and bases ionize/dissociate in water

  2. Basic (alkaline) solutions have bitter taste and are slippery.Ex.: soaps, “draino,” many household cleaning products Acidic solutions have sour taste (tartness).Ex.: citric acid in lemons, limes, oranges; acetic acid in vinegar

  3. Acid, Base or Salt? NaCl NaOH Ba(OH)2 HNO3 H2SO4 CaO HCl Mg(OH)2 NH3 LiOH LiF

  4. Acid-Base Reactions (review) Remember that… (add this to your notes) Acid + Base  Water + Salt Ex.: HCl + NaOH  H2O + NaCl This is a double replacement reaction This is a neutralization reaction Because H+ and OH-  H2O

  5. Naming Acids (review)

  6. A. Acids and Bases – Two Models • The Arrhenius Model (older) – Dissociation Reactions • Acid – produces hydrogen ions (H+) in aqueous solution H2O HCl(s)  H+(aq) + Cl- (aq) • Base – produces hydroxide ions (OH-) in aqueous solution H2O NaOH(s)  Na+(aq) + OH-(aq)

  7. A. Acids and Bases – Two Models • The Bronsted-Lowry Model (newer) – Dissociation & Reaction with Water • Acid – proton donor • Base – proton acceptor • The general reaction for an acid dissolving in water is

  8. A. Acids and Bases • The Bronsted-Lowry Model • Water acts as a base accepting a proton from the acid. • Forms hydronium ion (H3O+)

  9. A. Acids and Bases • The Bronsted-Lowry Model H+ NaOH + H2O Na+ + OH- + H2O • Water acts as an acid, donating a proton to the base. • Forms water molecule

  10. Ammonia is a base because it accepts a proton and becomes the ammonium ion: NH3 + H+ NH4+ Ammonia ammonium, a polyatomic cation

  11. A. Acids and Bases • The Bronsted-Lowry Model • Conjugate acid-basepairs

  12. The Bronsted-Lowry Model - Identifying Acid-Base Pairs Do the two substancesdiffer by a single proton? HF, F- conjugate pair: HF  H+ + F- NH4+, NH3 conjugate pair: NH4+ H+ + NH3 HCl, H2O not a conjugate pair: Conj. base of HCl: Cl- Conj. acid of H2O: H3O+

  13. The Bronsted-Lowry Model - Writing Conjugate Bases The acid and its conjugate base must differ by a single proton. Acid proton + conjugate base • HClO4 H+ + ClO4- • H3PO4  H+ + H2PO4- • CH3NH3+  H+ + CH3NH2

  14. Try to show the dissociation of each acid below into a proton and a conjugate base. Acid proton + conjugate base • H2CO3 H+ + HCO3- • H3BO3  H+ + H2BO3- • H3PO3 H+ + H2PO3- • HNO2  H+ + NO2-

  15. Learning Goals To understand the concept of acid strength

  16. B. Acid Strength • Strong acid – completely ionizes / dissociates • Forward reaction predominates • Weak acid – most of the acid molecules remain intact

  17. B. Acid Strength

  18. B. Acid Strength • A strong acid contains a relatively weak conjugate base. • Water molecules compete with the base for the protons: a weak base loses (dissociation happens, strong acid), a strong base wins (little dissociation, weak acid)

  19. B. Acid Strength • Common strong acids are • Sulfuric acid, H2SO4 • Hydrochloric acid, HCl • Nitric acid, HNO3 • Perchloric acid, HClO4 • * Strong acids are strong electrolytes • good conductivity *

  20. B. Acid Strength / Acid Types • Oxyacid – acidic proton is attached to an oxygen atom • Organic acid – have a carbon atom backbone and commonly contain the carboxyl group • Typically a weak acid

  21. Acid Strength / Acid Types • Monoprotic acids can furnish only one proton. Ex.: HCl  H+ + Cl- • Diprotic acids can furnish two protons.Ex.: H2SO4 2H+ + SO42- • Hydrohalic acids contain H attached to a halogen.Ex.: HCl (strong), HF (weak)

  22. B. Acid Strength

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