Lecture12221

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Lecture12221

  1. 1. Chemical Reactions: Acid-Base Lecture 12
  2. 2. Acid-base reactions everywhere.
  3. 3. Acid-base reactions:
  4. 4. An acid is a substance that produces H + ions when dissolved in water: HX  H + (aq) + X - (aq)
  5. 5. A base is a substance that produces OH - ions when dissolved in water: MOH  M + (aq) + OH - (aq)
  6. 6. Strong acids and strong bases dissociate completely into ions when dissolved in water. They conduct a current well.
  7. 9. Weak acids and weak bases dissociate into ions very little when dissolved in water. They conduct only a small current.
  8. 10. Strong and weak acids
  9. 11. The key event <ul><li>Molecular: 2HCl (aq) + Ba(OH) 2 (aq)  BaCl 2(aq) + 2H 2 O (l) </li></ul><ul><li>Total ionic: 2H + (aq) + 2Cl - (aq) + Ba 2+ (aq) + 2OH - (aq)  Ba 2 + (aq) + 2Cl - (aq) + 2H 2 O (l) </li></ul><ul><li>Net ionic: 2H + (aq) + 2OH - (aq)  2H 2 O (l) </li></ul><ul><li>or H + (aq) + OH - (aq)  H 2 O (l) </li></ul>
  10. 12. The key event:
  11. 13. The key event in all aqueous reactions between a strong acid and a strong base is that an H + ion from the acid and an OH - ion from the base form a water molecule.
  12. 14. The key event
  13. 15. Acid-base reactions occur through the electrostatic attraction of ions and their removal from solution in the formation of the product.
  14. 16. An acid and a base are the reactants in the reaction of neutralization.
  15. 17. A salt solution and water are the products in the reaction of neutralization.
  16. 18. A salt is a substance, an ionic compound that results from the reaction of an acid and a base.
  17. 19. The cation comes from the base, the anion comes from the acid: <ul><li>H Cl (aq) + Na OH (aq)  NaCl (aq) + H 2 O (l) </li></ul><ul><li>H NO 3 (aq) + K OH (aq)  KNO 3 (aq) + H 2 O (l) </li></ul><ul><li>H 3 PO 4 (aq) + 3 Na OH (aq)  Na 3 PO 4 (aq) + 3H 2 O (l) </li></ul><ul><li>H 2 SO 4 (aq) + Ba (OH) 2(aq)  BaSO 4 (s) + 2H 2 O (l) </li></ul>
  18. 20. Acid-base reaction: Acid + Base  Salt + Water
  19. 21. Acid-base reactions are double-displacement reactions, also called double-replacement and metathesis reactions. The ions are exchanging partners.
  20. 22. A sample problem on writing ionic equations for acid-base reactions.
  21. 23. Titration is a process of finding the quantity of a given chemical by the addition of a liquid reagent of known strength, and measuring the volume of that reagent necessary to cause a reaction that changes the form of the chemical in question.
  22. 24. In any titration, one solution of known concentration is used to determine the concentration of another solution through a monitored reaction.
  23. 25. Titration technique
  24. 26. An acid-base indicator is a substance whose color is different in acid than in base.
  25. 27. There are plenty of indicators
  26. 28. Litmus paper
  27. 29. The equivalence point in the titration occurs when all the moles of H + ions present in the original volume of acid solution have reacted with an equivalent number of moles of OH - ions added from the buret.
  28. 30. The end point in the titration occurs when a tiny excess of OH - ions changes the indicator permanently to its color in base.
  29. 31. In calculations, we assume that the amount of base needed to reach the end point is the same as the amount needed to reach the equivalence point.
  30. 32. There’s some strong acid in our stomachs
  31. 33. A sample problem on finding the concentration of acid from an acid-base titration.
  32. 34. HCl transfers its proton to H 2 O
  33. 35. An acid-base reaction is a proton transfer process.
  34. 36. <ul><li>Thomas Martin Lowry (1874-1936), </li></ul><ul><li>British scientist </li></ul>
  35. 37. <ul><li>Johannes Nicolaus Brønsted (1879-1947), </li></ul><ul><li>Danish scientist </li></ul>
  36. 38. Acid is a molecule or an ion that donates a proton.
  37. 39. Base is a molecule or an ion that accepts a proton.
  38. 40. In acid-base reactions H 3 O + acts as as the acid and OH - acts as the base.
  39. 41. Gas-forming reactions are often acid-base, referring to Brønsted and Lowry.
  40. 42. A gas-forming reaction: <ul><li>2HCl (aq) + K 2 CO 3(aq)  2KCl (aq) + [H 2 CO 3(aq) ] </li></ul><ul><li>[H 2 CO 3(aq) ]  H 2 O (l) + CO 2(g) </li></ul><ul><li>Overall: </li></ul><ul><li>2HCl (aq) + K 2 CO 3(aq)  2KCl (aq) + H 2 O (l) + CO 2(g) </li></ul><ul><li>Net ionic: </li></ul><ul><li>H 3 O + (aq) + CO 2- 3(aq)  3H 2 O (l) + 3CO 2(g)  </li></ul><ul><li>Carbonate ion acts as a base here. </li></ul>
  41. 43. Gas-forming reactions occur through the formation of gas and water because both products remove reactant ions from solution.
  42. 44. Ionic equations are written differently for the reactions of weak acids: they are shown undissociated.
  43. 45. THE END

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