Concept Attainment P H

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Concept Attainment P H

  1. 1. <ul><li>pH </li></ul>
  2. 2. REVIEWING SOME THINGS:
  3. 3. Arrhenius Theory of Acids and Bases <ul><ul><li>An acid is a substance that produces H+ ions in solution </li></ul></ul><ul><ul><li>A base is a substance that produces OHˉ ions in solution </li></ul></ul><ul><ul><li>Neutralization can be represented by: </li></ul></ul><ul><ul><li>Arrhenius theory does not recognize the contribution of the solvent in the ionization of the solute </li></ul></ul><ul><ul><li>It fails to explain weak bases such as carbonate (CO 3 2- ), and ammonia (NH 3 ) </li></ul></ul>HCl (g) H + (aq) + Clˉ (aq) H 2 O NaOH (s) Na + (aq) + OHˉ (aq) H 2 O H + (aq) + OHˉ (aq) H 2 O (l)
  4. 4. Br ø nsted Lowry Acid/Base Theory NaOH(s) + H 2 O(l) Na + (aq) + OHˉ(aq) HBr(g) + H 2 O(l) H 3 O + (aq) + Brˉ(aq) <ul><li>For our purposes H 3 O + and H + can be considered equivalent terms </li></ul><ul><li>Neutralization can be represented by: </li></ul>H 3 O + (aq) + OHˉ (aq) 2 H 2 O (l)
  5. 5. Br ø nsted Lowry Acid/Base Theory <ul><li>The main advantage of the Br ø nsted Lowry Theory is in its treatment of weak bases </li></ul><ul><ul><ul><li>An acid is a proton (H + ) donor </li></ul></ul></ul><ul><ul><ul><li>A base is a proton (H + ) acceptor </li></ul></ul></ul><ul><ul><li>Since NH 3 is a weak base, the reverse reaction should also be considered </li></ul></ul><ul><ul><li>This reversible reaction may be written as follows: </li></ul></ul>NH 3 + H 2 O NH 4 + + OHˉ conjugate acid conjugate base acid base NH 3 + H 2 O NH 4 + + OHˉ base acid NH 4 + + OHˉ NH 3 + H 2 O base acid
  6. 6. Review Question <ul><li>Identifying Br ø nsted-Lowry Acids and Bases and their Conjugates </li></ul>Question: For each of the following chemical equations, identify the acids and bases in both the forward and reverse reactions. i) HClO 2 + H 2 O ClO 2 ˉ + H 3 O + ii) OClˉ + H 2 O HOCl + OHˉ iii) NH 3 + H 2 PO 4 ˉ NH 4 + + HPO 4 2 ˉ conjugate acid conjugate base acid base conjugate acid conjugate base acid base conjugate acid conjugate base acid base
  7. 7. Last two things <ul><li>Concentration – how much of something is contained in a certain amount of solution </li></ul><ul><li>Molarity – a chemical means of measuring concentration </li></ul>
  8. 8. Concentration is measured in M <ul><li>[C 6 H 12 O 6 ] = 5 M  “Five Molar glucose” </li></ul><ul><li>[C 6 H 12 O 6 ] = 2 M  “Two Molar glucose” </li></ul><ul><li>[C 6 H 12 O 6 ] = 0.5 M  “0.5 Molar glucose” </li></ul><ul><li>[C 6 H 12 O 6 ] = 0.2 M  “0.2 Molar glucose” </li></ul><ul><li>Which of these is the most concentrated? </li></ul><ul><li>Which of these is the least concentrated? </li></ul>
  9. 9. What happens when the concentration gets really small? <ul><li>[C 6 H 12 O 6 ] = 0.00001 M </li></ul><ul><li>[C 6 H 12 O 6 ] = 0.00000001 M </li></ul><ul><li>[C 6 H 12 O 6 ] = 0.00000000000001 M </li></ul><ul><li>We bring back SCIENTIFIC NOTATION!!! </li></ul><ul><li>0.00001 M = 1 x 10 -5 M </li></ul><ul><li>0.00000001 M = 1 x 10 -8 M </li></ul><ul><li>0.00000000000001 M = 1 x 10 -14 M </li></ul>
  10. 10. Let’s apply this concentration & scientific notation stuff to Acids/Bases <ul><li>[HCl] = 0.00001 M </li></ul><ul><li>[CH 3 COOH] = 0.00000000000001 M </li></ul><ul><li>[HCl] = 1 x 10 -5 M </li></ul><ul><li>[CH 3 COOH] = 1 x 10 -14 M </li></ul>
  11. 11. Let’s apply this concentration & scientific notation stuff to Acids/Bases <ul><li>[HCl] & [CH 3 COOH] are acids </li></ul><ul><ul><li>Acids  generate H + </li></ul></ul><ul><li>So, </li></ul><ul><li>[HCl] = 1 x 10 -5 M  [H + ] = 1 x 10 -5 M </li></ul><ul><li>[CH 3 COOH] = 1 x 10 -14 M  [H + ] = 1 x 10 -14 M </li></ul>
  12. 12. Now, let’s use the scientific notation… <ul><li>Rank the following from least to greatest concentration of Hydrogen ions </li></ul><ul><li>[HCl] = 1 x 10 -6 M </li></ul><ul><li>[CH 3 COOH] = 1 x 10 -14 M </li></ul><ul><li>[HNO 3 ] = 1 x 10 -2 M </li></ul><ul><li>[HBr] = 1 x 10 -12 M </li></ul><ul><li>[HClO 3 ] = 1 x 10 -3 M </li></ul><ul><li>[HF] = 1 x 10 -13 M </li></ul>
  13. 13. <ul><li>[CH 3 COOH] = 1 x 10 -14 M </li></ul><ul><li>[HF] = 1 x 10 -13 M </li></ul><ul><li>[HBr] = 1 x 10 -12 M </li></ul><ul><li>[HCl] = 1 x 10 -6 M </li></ul><ul><li>[HClO 3 ] = 1 x 10 -3 M </li></ul><ul><li>[HNO 3 ] = 1 x 10 -2 M </li></ul>Regardless of the acid’s identity, the concentrations of H + ions rank as follows:
  14. 14. <ul><li>[H + ] = 1 x 10 -14 M </li></ul><ul><li>[H + ] = 1 x 10 -13 M </li></ul><ul><li>[H + ] = 1 x 10 -12 M </li></ul><ul><li>[H + ] = 1 x 10 -6 M </li></ul><ul><li>[H + ] = 1 x 10 -3 M </li></ul><ul><li>[H + ] = 1 x 10 -2 M </li></ul><ul><li>It means the same thing!! </li></ul>So, we might as well just write…
  15. 15. Now, for the NEW idea: pH <ul><li>See if you can figure out what is going on in the next slides… </li></ul>
  16. 16. Part 1: Define a logarithm <ul><li>When the [H + ] = </li></ul><ul><li>1 x 10 -14 M -14 </li></ul><ul><li>1 x 10 -13 M -13 </li></ul><ul><li>1 x 10 -12 M -12 </li></ul><ul><li>1 x 10 -11 M -11 </li></ul><ul><li>1 x 10 -10 M -10 </li></ul><ul><li>1 x 10 -9 M -9 </li></ul><ul><li>1 x 10 -8 M -8 </li></ul><ul><li>1 x 10 -7 M -7 </li></ul><ul><li>1 x 10 -6 M -6 </li></ul><ul><li>1 x 10 -5 M -5 </li></ul><ul><li>1 x 10 -4 M -4 </li></ul><ul><li>1 x 10 -3 M -3 </li></ul><ul><li>1 x 10 -2 M -2 </li></ul><ul><li>1 x 10 -1 M -1 </li></ul><ul><li>The logarithm of [H + ] = </li></ul>
  17. 17. Part 2: How do we change the log result into a positive number? Multiply the log by -1 to change it to positive <ul><li>When [H + ] = Log [H + ] = - Log [H + ] = </li></ul><ul><li>1 x 10 -14 M -14 14 </li></ul><ul><li>1 x 10 -13 M -13 13 </li></ul><ul><li>1 x 10 -12 M -12 12 </li></ul><ul><li>1 x 10 -11 M -11 11 </li></ul><ul><li>1 x 10 -10 M -10 10 </li></ul><ul><li>1 x 10 -9 M -9 9 </li></ul><ul><li>1 x 10 -8 M -8 8 </li></ul><ul><li>1 x 10 -7 M -7 “times -1” 7 </li></ul><ul><li>1 x 10 -6 M -6 6 </li></ul><ul><li>1 x 10 -5 M -5 5 </li></ul><ul><li>1 x 10 -4 M -4 4 </li></ul><ul><li>1 x 10 -3 M -3 3 </li></ul><ul><li>1 x 10 -2 M -2 2 </li></ul><ul><li>1 x 10 -1 M -1 1 </li></ul>
  18. 18. It’s LOG!!!! <ul><li>So, what does a log do? </li></ul><ul><ul><li>It changes a number that is written in scientific notation into the EXPONENT of the scientific notation </li></ul></ul><ul><li>What does -log do? </li></ul><ul><ul><li>It changes a number that is written in scientific notation with a NEGATIVE EXPONENT into a POSITIVE NUMBER ALONE </li></ul></ul>
  19. 19. Part 3: pH <ul><li>When the [H + ] = </li></ul><ul><li>1 x 10 -14 M 14 </li></ul><ul><li>1 x 10 -13 M 13 </li></ul><ul><li>1 x 10 -12 M 12 </li></ul><ul><li>1 x 10 -11 M 11 </li></ul><ul><li>1 x 10 -10 M 10 </li></ul><ul><li>1 x 10 -9 M 9 </li></ul><ul><li>1 x 10 -8 M 8 </li></ul><ul><li>1 x 10 -7 M 7 </li></ul><ul><li>1 x 10 -6 M 6 </li></ul><ul><li>1 x 10 -5 M 5 </li></ul><ul><li>1 x 10 -4 M 4 </li></ul><ul><li>1 x 10 -3 M 3 </li></ul><ul><li>1 x 10 -2 M 2 </li></ul><ul><li>1 x 10 -1 M 1 </li></ul><ul><li>The pH = </li></ul>
  20. 20. So, what is pH ? <ul><li>A mathematical operation </li></ul><ul><ul><li>Just like Sum, Difference, Product, etc. </li></ul></ul><ul><li>It does the same thing that taking the –log of a number does!!! </li></ul><ul><ul><li>The “p” means ‘take the negative log of’ </li></ul></ul><ul><ul><li>The H stands for [H + ] </li></ul></ul><ul><ul><li>Thus, </li></ul></ul><ul><ul><li>pH = -log [H + ] </li></ul></ul>
  21. 21. Find the pH of each of the following <ul><li>Concentration </li></ul><ul><li>[HCl] = 1 x 10 -6 M </li></ul><ul><li>[CH 3 COOH] = 1 x 10 -14 M </li></ul><ul><li>[HNO 3 ] = 1 x 10 -2 M </li></ul><ul><li>[HBr] = 1 x 10 -12 M </li></ul><ul><li>[HClO 3 ] = 1 x 10 -3 M </li></ul><ul><li>[HF] = 1 x 10 -13 M </li></ul>pH 6 14 2 12 3 13
  22. 22. What did you notice about the pH scale compared to concentration? The smaller the pH the higher the concentration of the [H + ]
  23. 23. Let’s try our using pH to rank acid strength
  24. 24. Now, let’s use the scientific notation… <ul><li>Rank the following from least to greatest concentration of Hydrogen ions </li></ul><ul><li>pH of HCl = 6 </li></ul><ul><li>pH of CH 3 COOH = 2 </li></ul><ul><li>pH of HNO 3 = 3 </li></ul><ul><li>pH of HBr = 11 </li></ul><ul><li>pH of HClO 3 = 8 </li></ul><ul><li>pH of HF = 10 </li></ul>
  25. 25. The following are ranked from LEAST to GREATEST [H + ] <ul><li>pH of HBr = 11 </li></ul><ul><li>pH of HF = 10 </li></ul><ul><li>pH of HClO 3 = 8 </li></ul><ul><li>pH of HCl = 6 </li></ul><ul><li>pH of HNO 3 = 3 </li></ul><ul><li>pH of CH 3 COOH = 2 </li></ul>The smaller the pH the higher the concentration of the [H + ]
  26. 26. Why use pH? <ul><li>It’s much more convenient way of measuring [H + ] than using scientific notation </li></ul><ul><ul><li>It transforms the negative exponents into positive numbers </li></ul></ul><ul><li>We can use pH to talk about acid strength </li></ul>
  27. 27. The pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14
  28. 28. The Acid Concentration Scale When [H + ] = 1 x 10 to the… -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14
  29. 29. Let’s see if the pH concept makes sense to you <ul><li>What does the “H” part of pH mean? </li></ul><ul><li>What does the “p” part of pH mean? </li></ul><ul><li>What does taking the log of a number do? </li></ul><ul><li>What does taking the –log of a number do? </li></ul><ul><li>Could pH work for ions other than [H + ]? </li></ul><ul><ul><li>Could we take a pOH perhaps??? </li></ul></ul>
  30. 30. pOH: the flip-side of pH <ul><li>Works JUST LIKE pH, except we are talking now about the [OH - ] instead of [H + ] </li></ul><ul><li>What is the pOH of a NaOH solution that is 1 x 10 -3 M? </li></ul><ul><li>pOH = 3 </li></ul>
  31. 31. The pOH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14
  32. 32. The Base Concentration Scale When [OH - ] = 1 x 10 to the… -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14
  33. 33. Find the pOH of each of the following <ul><li>Concentration </li></ul><ul><li>[NaOH] = 1 x 10 -6 M </li></ul><ul><li>[KOH] = 1 x 10 -14 M </li></ul><ul><li>[LiOH] = 1 x 10 -2 M </li></ul>pOH 6 14 2
  34. 34. What’s the relationship between pH and pOH? <ul><li>pH + pOH = 14 ALWAYS!!! </li></ul>
  35. 35. pH and pOH <ul><li>The potential of the hydrogen ion was defined in 1909 as the negative of the logarithm of [H + ]. </li></ul>pH = -log[H 3 O + ] pOH = -log[OH - ] [H 3 O + ][OH - ]= 1.0x10 -14 pH + pOH = 14
  36. 36. Sample Question <ul><li>Calculate the pH and pOH of 0.10 M HBr </li></ul>HBr + H 2 O H 3 O + + Brˉ For our purposes H 3 O + and H + can be considered equivalent terms pH = -log [H + ] pH = -log (0.1) pH = 1.0 Since pH + pOH = 14 1.0 + pOH = 14 pOH = 13
  37. 37. Another Sample Question <ul><li>Calculate the pH of 0.10 M KOH </li></ul>KOH is a strong base and will fully dissociate; [OHˉ] = 0.10M Method # 2 Calculate pOH pOH = -log [OH ˉ ] pOH = -log (0.1) pOH = 1.0 pH + pOH = 14 pH + 1 = 14 pH = 13 Calculate pH
  38. 38. Why pH/pOH?? Autoprotolysis of Water H 2 O + H 2 O H 3 O + + OH - base acid c. acid c. base K c = [H 2 O][H 2 O] [H 3 O + ][OH - ] K W = K c [H 2 O][H 2 O] = = 1.0x10 -14 [H 3 O + ][OH - ] K W = = 1.0x10 -14 [H 3 O + ][OH - ]

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