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Chapter 14

Chapter 14. Acids and Bases. Acid/Base Theories. Arrhenius Theory Acids produce H + ions in solution Bases produce OH - ions in solution Downside Must be in solution and must have those ions Bronsted-Lowry Theory Acids are H + donors (Proton donors)

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Chapter 14

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  1. Chapter 14 Acids and Bases

  2. Acid/Base Theories • Arrhenius Theory • Acids produce H+ ions in solution • Bases produce OH- ions in solution • Downside • Must be in solution and must have those ions • Bronsted-Lowry Theory • Acids are H+ donors (Proton donors) • Bases are H+ acceptors (Proton acceptors)

  3. Vocabulary • H+ is the hydrogen ion • Just a proton • H3O+ is a hydronium ion • It is the way H+ exists in water • Water accepts a hydrogen ion and becomes H3O+ • Either way is fine the first is just easier

  4. Conjugates Acid/Base Pairs • Conjugate Acid is formed when a base gains a proton • Conjugate Base is what remains after an acid donates a proton • Ex – HNO3 + H2O  H3O+ + NO3-

  5. General Form for Acids and Bases HA + B  A- + BH+ • HA is an acid • B is a base • A- is the conjugate base • Just the negative ion of the acid • BH+ is the conjugate acid • Just the base plus a hydrogen

  6. Strong and Weak Acids • Strong acids completely ionize in solution • Nitric, Perchloric, Sulfuric, Hydrochloric, Hydrobromic, Hydroiodic • Weak Conjugate bases • Weak Acids only partially ionize in solution • Every other acid • Equilibrium is established in the ionization • Weak acids have Ka values • Strong Conjugate bases

  7. Acid Dissociation Constant, Ka HA(aq) + H2O  A- + H3O+ • For weak acids equilibrium is established • Equilibruim constant is Ka • Ka=[A-][H3O+]/[HA] • Values tend to be small • Because CB is fairly strong • Strong acids do not have Ka values.

  8. Acid Terms • Monoprotic – One acidic hydrogen • Polyprotic – Many acidic hydrogens • Diprotic – Two acidic hydrogens • Triprotic – Three acidic hydrogens • Oxyacid – Acid that has an acidic hydrogen attached to an oxygen • Organic Acid – Acid that has the acidic hydrogen attached to the carboxyl group

  9. Water As An Acid and Base • Water is amphoteric – Both an acid and base H2O + H2O  H3O+ + OH- • Equilibrium system that always has the same value • Called Kw

  10. Autoionization of Water, Kw H2O + H2O  H3O+ + OH- • Kw = [H3O+] [OH-] • In pure water the products have the same concentration, 1.00x10-7M • Value of Kw = 1.00x10-14 at 25ºC • Concentrations can change is acid or base is added

  11. Acid, Base, or Neutral • If the concentration of H+ = OH- • Neutral • If the concentration of H+ > OH- • Acidic • If the concentration of H+ < OH- • Basic

  12. What is the hydrogen ion concentration when the hydroxide ion concentration is 1.00x10-5M

  13. What is the hydroxide ion concentration when the when the concentration of nitric acid is 0.0010M?

  14. Homework • P. 704 30, 32, 33, 35, 39ab,40ab

  15. Logarithms • The logarithm of a number to a given base (commonly 10) is the power or exponent to which the base must be raised in order to produce the number. • SAY WHAT!

  16. Examples • If your question says log 100 = x It is saying to what power must 10 be raised to equal 100 10x = 100 102 = 100 So x = 2

  17. Examples log 1 = x x = 0 log 10 = x x = 1 log 1000 = x x = 3 log 1x106 = x x = 6

  18. Examples • Logarithms can also be used for numbers smaller than 1 log 0.1 = x x = -1 log 0.01 = x x = -2 log 1x10-5 x = -5

  19. Examples • If they are not easy to calculate you can do it on your calculator log 15 = x You can approximate it between . . . • Type log 15 on your calculator x = 1.18

  20. Examples • If your question says log x = 7 It is saying 10 to the 7th power is what number 107 = 1x107 log x = 3 x = 1000 log x = -3 x = 0.001

  21. Tougher Examples log 234 = x x = 2.37 log x = -3.3 x = 5.0x10-4 -log 9.1x10-5 = x x = 4.0 -log x = 12.1 x = 7.9x10-13

  22. pH • Negative logarithm of the concentration of hydrogen ions in solution pH = -log [H+] • pH means power of Hydrogen • Measures how acidic or basic a solution is • pH scale typically goes from 0 to 14 • pH < 7 Acidic • pH > 7 Basic

  23. Highly acidic = low pH • Highly basic = high pH

  24. Significant Figures and pH • Digits after the decimal are the only ones that are significant in pH values pH = 4.44 2 Significant Figures pH = 10.874 3 Significant Figures • If your [H+] is 0.088 M your pH is 1.06

  25. Determining [H+] in solution • The concentration of a strong acid is equal to the H+ concentration. • 0.010 M HCl has an [H+] of 0.010 M • To obtain the [H+] for weak acids you must use equilibrium • Need Ka data • Discuss hydroxide later

  26. Other Info Turn Kw into a log equation pH + pOH = 14.00

  27. pH’s You MUST Know • When the [H+] is _______ the pH is _____ 0.10 M 1.00 0.0010M 3.00 1.0x10-6M 6.00 1.0x10-10M 10.00

  28. Find the pOH, [H+], [OH-] of lemon juice that has a pH of 2.48

  29. Determine the pH of 0.150M HCl

  30. Determine the pH of 2.3x10-3 M Hydrocyanic Acid HCN. Ka = 6.2x10-10

  31. Homework • Page 705 #’s 45,47,50,52,53,58

  32. Mixtures of Weak Acids • When there are mixtures of weak acids in solution determining the pH could be a difficult problem. • However • The acid with the largest Ka will control the pH of the solution

  33. Solutions of 0.10M HF (Ka = 7.2x10-4) and 0.10M HCN (Ka = 6.2x10-10) are mixed A) Which acid will control the pH of the solution? Why? B) What is the pH of the resulting solution.

  34. Percent Dissociation • Ratio of the concentration of the dissociated ions to the initial concentration • Found just like the doing the 5% check • Can be used to find pH and Ka

  35. A 0.25M solution of HClO is 20.% dissociated. A) What is the pH? B) What is the Ka value of the acid?

  36. Strong Bases • Strong bases are any compound containing the hydroxide ion • Group 1 hydroxides are very soluble • Group 2 less soluble but still strong • Group 2 have two hydroxides per mole • Be Careful

  37. Determine the pH of 0.022M Sr(OH)2

  38. Weak Bases • Organic Bases are weak bases. (Ammonia) • Contain Nitrogen (Amines) • CH3NH2 – Methylamine • Must have a lone pair of electrons • The hydroxide will come from water (CH3)3N + H2O

  39. Cont. • Weak bases have Kb values B + H2O BH+ + OH- • The conjugate acid of a weak base is stronger than water.

  40. Determine the pH of 15.0 M ammonia. The Kb is 1.8x10-5

  41. Homework • Page 705 #’s 62,63a,72,73,77ab,87

  42. Polyprotic Acids • Acids with more than one acidic hydrogen • Dissociate in a “stepwise” process H3PO4 H+ + H2PO4- Ka1 =7.5x10-3 H2PO4-  H+ + HPO4-2 Ka2 =6.2x10-8 HPO4-2  H+ + PO4-3 Ka3 =4.8x10-13 • Ka1 > Ka2 > Ka3 • Successive dissociation do not effect pH (except sulfuric acid)

  43. Determine the pH of 5.0M H3PO4 (Ka=7.5x10-3) and the [H2PO4-], [HPO4-2], [HPO4-3]

  44. Sulfuric Acid • Sulfuric acids has two dissociations • The first is strong • The second is weak • The second dissociation is quite strong, but it is not complete H2SO4 H+ + HSO4- (Strong) HSO4-  H+ + SO4-2 Ka = 1.2x10-2

  45. Continued • When you write sulfuric acid in net ionic equations only use the first equation H2SO4 H+ + HSO4- • The second dissociation only needs to be considered in dilute solutions. • A 1.0M solution of sulfuric acid will have a lower pH than a 1.0M solution of HCl

  46. Acid / Base Properties of Salts • Some salts have acid base properties • Make a solution have a pH below or above 7 • Some have no acid base properties • Make a solution with a pH of 7

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