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Acids & Bases

Acids & Bases. Intro to Acids and Bases (Properties). ACIDS SOUR TASTE TURN LITMUS RED VINEGAR, MILK, SODA , APPLES, CITRUS FRUITS . BASES BITTER TASTE TURN LITMUS BLUE SLIPPERY FEEL AMMONIA, LYE, ANTACID, BAKING SODA. H. H. –. +. O. O. Cl. Cl. H. H. H. H.

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Acids & Bases

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  1. Acids & Bases

  2. Intro to Acids and Bases(Properties) • ACIDS • SOUR TASTE • TURN LITMUS RED • VINEGAR, MILK, SODA , APPLES, CITRUS FRUITS • BASES • BITTER TASTE • TURN LITMUS BLUE • SLIPPERY FEEL • AMMONIA, LYE, ANTACID, BAKING SODA

  3. H H – + O O Cl Cl H H H H Definitions of Acids and Bases • Arrhenius - In aqueous solution… • Acidsform hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– acid

  4. H H – + N O O N H H H H H H H H Definitions of Acids and Bases • Arrhenius - In aqueous solution… • Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- base

  5. conjugate base conjugate acid Definitions of Acids and Bases • Brønsted-Lowry • Acidsare proton (H+) donors. • Bases are proton (H+) acceptors. HCl + H2O  Cl– + H3O+ acid base

  6. Conjugate Acids and Bases H2O + HNO3 H3O+ + NO3– B A CA CB

  7. Conjugate Acids and Bases NH3 + H2O  NH4+ + OH- B A CA CB • Amphoteric - can be an acid or a base.

  8. Conjugate Acids and Bases F - H2PO4- H2O HF H3PO4 H3O+ • Give the conjugate base for each of the following: • Polyprotic - an acid with more than one H+

  9. Conjugate Acids and Bases Br - HSO4- CO32- HBr H2SO4 HCO3- • Give the conjugate acid for each of the following:

  10. Definitions of Acids and Bases • Lewis • Acidsare electron pair acceptors. • Bases are electron pair donors. Lewis base Lewis acid

  11. - + Strength of Acids and Bases • Strong Acid/Base • 100% ionized in water • strong electrolyte HCl HNO3 H2SO4 HBr HI HClO4 NaOH KOH Ca(OH)2 Ba(OH)2

  12. - + Strength of Acids and Bases • Weak Acid/Base • does not ionize completely • weak electrolyte HF CH3COOH H3PO4 H2CO3 HCN NH3

  13. Oxyacids, Carboxylic Acids, Polyprotic acids • Oxyacids – acids in which the acidic proton is attached to an oxygen atom (many of the above acids we talked about are of this type – may be strong or weak) • Carboxylic acids – organic acids with the “COOH” group – are usually weak • Polyprotic acids – acids that have more than one acidic proton (can give up more than one H+)

  14. Acid/Base Equilibrium

  15. Equilibrium Constant for Water(Ion Product Constant) H2O(l) ↔ H+(aq) + OH-(aq) From what we know about equilibrium expressions: Remember, we include gaseous and aqueous species, but not liquids and/or solids Kw = 1.0 x 10-14

  16. Acid Dissociation Constant HA(aq) + H2O(l) ↔ H3O+(aq) + A-(aq) ACIDBASE ↔ C ACID C BASE The equilibrium expression for this reaction is If Ka is large  strong acid (more complete dissociation) If Ka is small  weak acid

  17. Base Dissociation Constant B(aq) + H2O(l) ↔ BH+(aq) + OH-(aq) BASEACID ↔ C ACID C BASE The equilibrium expression for this reaction is If Kb is large  strong base (more complete dissociation) If Kb is small  weak base

  18. pH Refer to the pH diamond for help with the calculations

  19. pouvoir hydrogène (Fr.) “hydrogen power” pH Scale 14 0 7 INCREASING BASICITY INCREASING ACIDITY NEUTRAL pH = -log[H+]

  20. pH Scale pH of Common Substances

  21. pH Scale & Calculations pH = -log[H+] pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14

  22. pH Scale • What is the pH of 0.050 M HNO3? pH = -log[H+] pH = -log[0.050] pH = 1.3 Acidic or basic? Acidic

  23. pH Scale • What is the molarity of HBr in a solution that has a pOH of 9.6? pH + pOH = 14 pH + 9.6 = 14 pH = 4.4 [H+] = 10-pH [H+] = 10-4.4 [H+] = 4.0  10-5 M HBr Acidic

  24. Titration and Neutralization

  25. Neutralization • Chemical reaction between an acid and a base. • Products are a salt (ionic compound) and water.

  26. 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.

  27. standard solution unknown solution Titration • Titration • Analytical method in which a standard solution is used to determine the concentration of an unknown solution.

  28. Titration • Equivalence point (endpoint) • Point at which equal amounts of H+ and OH- have been added. • Determined by… • indicator color change • Dramatic change in pH

  29. Titration moles H+ = moles OH- MVn = MVn M: Molarity V: volume n: # of H+ ions in the acid or OH- ions in the base

  30. Titration • 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4. H2SO4 (H+) M = ? V = 50.0 mL n = 2 KOH (OH-) M = 1.3M V = 42.5 mL n = 1 MVn = MVn M(50.0mL)(2) =(1.3M)(42.5mL)(1) M = 0.55M H2SO4

  31. Buffers

  32. Buffered Solutions • Buffers are solutions that resist changes in pH when limited amounts of acid or base are added • A buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. • The mixture of ions in the buffer resists changes in pH by reacting with any H+ or OH- ions added to the buffered solution

  33. Buffers (cont’d) • The buffer capacity is the amount of acid or base a buffer solution can absorb without a significant change in pH. • A buffer system is most effective when the concentrations of the conjugate acid-base pair are equal or nearly equal. (Adapted from Mrs. J’s chemistry lecture notes)

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