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Acids/Bases/ch 15

Acids/Bases/ch 15. Acid/base. Electrolyte—any substance which will form ions in solution and conduct electricity Three classes of electrolytes: A) Acids B) Bases C) Salts. Acid/Base. Properties of Acids: A) taste sour B) turn litmus red C) clear in phenolphthalein

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Acids/Bases/ch 15

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  1. Acids/Bases/ch 15

  2. Acid/base • Electrolyte—any substance which will form ions in solution and conduct electricity • Three classes of electrolytes: • A) Acids • B) Bases • C) Salts

  3. Acid/Base • Properties of Acids: • A) taste sour • B) turn litmus red • C) clear in phenolphthalein • D) react with water to form H3O+ • E) react with metals to form H2 gas

  4. Acid/Base • Strong acids—dissociate in water to form many ions “go to completion”. Have high Ka • Ex: HCl(aq) + H2O  H3O+(aq) + Cl-(aq) • Only 6 strong acids exist: • HCl HBr HI HNO3 • HClO4 H2SO4 • Show the dissociation on the board for each.

  5. Acid/Base • Monoprotic acids---acids with only one hydrogen to ionize • HCl, HBr, HI, HF, HNO3, HClO4,CH3COOH

  6. Acid/Base • Diprotic acids—those with 2 “H” to ionize • H2SO4 and H2CO3

  7. Acid and Base • Triprotic Acids—those with 3 “H” to ionize • H3PO4 Polyprotic acids---those with more than one “H” to ionize

  8. Acid/Base • Binary acids---those with only two elements • Ternary acids—those with “3” elements

  9. Acid --Base • Weak acids---- those which do NOT dissociate completely in water/ • Equilibrium is reached () • HF(aq) + H2O  H3O+(aq) + F-(aq) • Or • CH3COOH(aq) + H2O  H3O+(aq) + CH3COO-(aq)

  10. Acid/Base • Properties of Bases: • A) taste bitter • B) turn litmus blue • C) turn pink in phenolpthalein • D) release OH- in solution • E) feel slippery to the touch • F) forms alkaline solutions

  11. Acid -base • Strong bases---dissociate completely in water • Strong bases are: bases with cations from groups 1 or 2 • ex: NaOH, KOH, LiOH, Ca(OH)2, Mg(OH)2

  12. Acid/Base • Ex: • NaOH(aq) Na+(aq) + OH-(aq) • Ca(OH)2(aq)  Ca+2(aq) + 2OH-(aq) • ********note that when strong bases dissociate all OH- are released

  13. Acid/Base • Weak bases—dissociate only a small amount and few ions form. Equilibrium is reached () • NH4OH(aq)  NH4+(aq) + OH-(aq) or Al(OH)3(aq)  Al+3(aq) + 3OH-(aq)

  14. Acid/Base • Neutralization: (double replacement) • Acid + base => water + salt • HCl + KOH => HOH + KCl • Write the balanced equation for? • Sulfuric acid reacts with calcium hydroxide

  15. Acid/Base • Acids will always form the hydronium ion • (H3O+) when put into water. • Draw the structural formula on board • Structural formula shows bonding and where each atom is located in the molecule.

  16. Acid/Base • Three classes of Acids and Bases: • A) Arrhenius • B) Bronsted-Lowry • C) Lewis

  17. Acid/Base • Arrhenius: • Acid: releases H+ into solution (HBr, HCl, etc) • Base: releases OH- into solution (KOH, NaOH,etc)

  18. Acid/Base • Bronsted-Lowry: • Acid: a proton donor • Base: a proton acceptor • HCl(aq) + H2O  H3O+(aq) + Cl-(aq) • (Cl-) is the spectator ion ( does NOT participate in reaction)

  19. Acid/Base • H2SO4(aq) + H2O => H3O+(aq) + HSO4-(aq) • What is the spectator ion?

  20. Acid -Base • Conjugate base: of an acid is the part that remains after a proton has been released • (always a product) • HF + H2O => H3O+ + F- • F- is the conjugate base • Demo on the board

  21. Acid- Base • Conjugate acid- of a base is formed when the base accepts the proton from the acid • ( always a product) • H3O+ is the conjugate acid of the previous reaction H2SO4 + H2O => H3O+ + HSO4- acid base c. acid c. base

  22. Acid/Base • A B • HI _____ • CH3COOH ______ • H3O+ _______ • ______ OH- • ______ HSO4-

  23. Acid-Base • Lewis : • acid: an e- pair acceptor • base: an e- pair donor • BF3 + NH3 => F3BNH3 • Demo on board

  24. Acid/Base • Amphoteric: substance which acts as an acid or a base ex: water • Demo on board • hydrochloric acid + water => • ammonia + water =>

  25. Acid/Base • Anhydrous: Without water • Acidic anhydride---an oxide that will produce an acid when added to water • carbon dioxide + water => carbonic acid • Basic anhydride—an oxide that will produce a base when added to water • sodium oxide + water => sodium hydroxide

  26. pH Scale • Acid or base ? • pH scale is from 0-14 • less than 7 ----acid • Greater than 7---basic • pH 7 ---neutral • Pure water is neutral

  27. pH Scale • Acid /base indicators can be used to determine if a solution is an acid or a base. Acid base • Litmus red blue • Phenolphthalein clear pink • Phenol red yellow green • Different indicators will work at different pH levels

  28. Acid/Base • Phenolphthalein works best between 8.5 and 10. • Could you use Phenolphthalein on a solution with pH 6.5 ? Why? Why not?

  29. Acid/Base • Pure water will ionize only a small amount. • ( it will be at equilibrium) • HOH(l) H+(aq) + OH-(eq) • K(eq) = [H+][OH-] • Since it takes 107 liters of water to form 1 mole of hydroxide ion and 1 mole of hydrogen ion, its Molarity is 1Mol/107liters • M = 1 X 10-7 for each ion

  30. Acid/Base • The special equilibrium for water is : • Kw = [H+][OH-] • Kw = [ 1x 10-7][ 1 x 10-7] • Kw = 1 X 10 -14 • Kwalways = 1 x10-14 • ******note H+ is the same as H3O+

  31. Acid – Base • [H+] = [OH-] in pure water • If you know the [ ] of the H+ you can calculate the [ ] of the OH- and vice versa

  32. Acid-base • Ex: What is the [OH-] in a solution of .25M hydrochloric acid . • Step one: determine if acid is strong • Step two: write hydrogen ion concentration in exponential form • Step three: use Kw to solve the problem • Kw = [H+][OH-] • 1 x 10-14 = [ 2.5 x 10-1] [ OH-] • [OH-] = 1 X 10-14/ 2.5 X 10-1 • [OH-] = 4 X 10 -14

  33. What is the [H3O+] in a .004 M NaOH solution. Is this an acidic or basic solution?

  34. What is the [OH -] in a .50M solution of HNO3 solution?

  35. Acid - Base • Demo on the board • Page 541 (1-4)

  36. pH • pH can be calculated from the [H+] • pH = -log[H+] • Ex: What is the pH of a solution with: • [H3O+] = 1 X 10-3 • pH = -log(1 X 10-3) • pH = -1(-3) • pH = 3 • Demo on calculator

  37. pOH • pOH = -log [OH-] • What is the pOH of a solution that is .0001 M sodium hydroxide? • Sodium hydroxide is a strong base so it ionizes completely. • [OH-] = 1 X 10 -4 • pOH = -log ( 1 X 10-4) • pOH = -1(-4) • pOH = 4

  38. pH and pOH • pH + pOH = 14

  39. pH Calculate the pH of the following: a) [H+] = 3.0 X 10-8 b) [OH-] = 4.0 X 10-6 c) [H3O+] = 8.2 X 10-6 Determine for each example if it is acid, base, or neutral.

  40. pH • True or false: • As the [H3O+] increases the pH increases. • As the solution becomes more basic the [OH-] increases • As the pH increases the [OH-] increases • In pure water [H+] = [OH-]

  41. Titrations • Acid-base titration—process in which a neutralization reaction is used to determine the concentration of a solution with unknown molarity.

  42. Titrations • An acid base indicator showing the color change at the “end point” will be used. • End point—point in the titration in which the color of the solution changes • Equivalence point---the point at which the amount of acid will neutralize the base. Mols of [H+] = mols of [OH-]

  43. Titration • Titration curves: • Strong acid titrated with strong base (p551) • Weak acid titrated with strong base • Strong acid titrated with weak base • Plateau of each curve represents the part of the titration in which the hydrogen ion is neutralizing the hydroxide ion.

  44. Titrations • Solving titration problems: • VaMa = VbMb What is the molarity of a NaOH solution if 40.0 ml of the solution is neutralized by 35.6 ml of .24 M solution of HBr. VaMa = VbMb 35.6 ml x .24 M = 40.0ml X Mb Mb = .21 M

  45. How many milliliters of .005 M KOH is needed to neutralize 50 ml of .05M HNO3?

  46. Performing a titration page 552 and 553

  47. Buffer solutions: solutions which resist changes in pH • Blood needs to have pH from 7.35 to 7.45. • If below 7.35 you suffer acidosis • If above 7.45 you suffer alkalosis

  48. Acidosis: blood overwhelmed with too much acid ( leg cramps after exhausting excerise) • Alkalosis: blood has too little acid. ( hyperventilation ---body loses too much CO2)

  49. Buffer solution : is made from a WEAK acid and its conjugate base. This will neutralize the change in pH. • If the solution is “buffered” the addition of a small amount of acid or base will NOT change the pH

  50. Salts • Salt—an ionic compound composed of the cation of the base and the anion of the acid. May be soluble or insoluble. • Old book page 920---table ex: sulfuric acid reacts with calcium hydroxide. • Write the balanced equation • Classify the reaction • Name the salt • Determine if the salt is soluble or insoluble

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