Lecture 19.2- pH

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Section 19.2 Lecture for Honors & Prep Chemistry

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Lecture 19.2- pH

  1. 1. BELLWORK- Label pairs Identify the conjugate acid-base pairs a. H2S + H2O  HS- + H3O+ b. HClO4 + H2O  ClO4- + H3O+ c. NH3 + H2O  NH4+ + OH- d. H2O + HNO3  NO3- + H3O+
  2. 2. The pH scale measures the hydrogen ion concentration[H+] of a solution.
  3. 3. A pH of 7 is neutral A pH less than 7 is acidic (litmus is red) A pH greater than 7 is basic (litmus is blue) The pH scale ranges from below zero (very acidic) to above 14 (very basic)
  4. 4. The pH scale is not linear. The pH scale is logarithmic. pH = -log[H+] [H+] = 1.0 x 10-2 pH = 2 very acidic [H+] = 1.0 x 10-3 pH = 3 acidic A solution with pH of 2 contains 10 times as much H+ as a solution with pH of 3.
  5. 5. Calculate pH pH = -log [H+] [H+] = 1.0 x 10-7M [H+] = 5.0 x 10-5M
  6. 6. Calculate pH pH = -log [H+] [H+] = 1.0 x 10-7M pH= -(exponent) =7 [H+] = 5.0 x 10-5M
  7. 7. Calculate pH pH = -log [H+] [H+] = 1.0 x 10-7M pH= -(exponent) =7 [H+] = 5.0 x 10-5M pH is between 4&5
  8. 8. Calculate pH pH = -log [H+] [H+] = 1.0 x 10-7M pH= -(exponent) =7 [H+] = 5.0 x 10-5M pH is between 4&5 to CHECK with calculator 1.Enter concentration in calculator 2.Press log key 3.Change sign to positive OR in the reverse order depending on your calculator!
  9. 9. Calculate [H+] given pH pH = 7.0 pH= 8.5
  10. 10. Calculate [H+] given pH pH = 7.0 [H+]= 1x10-7 pH= 8.5
  11. 11. Calculate [H+] given pH pH = 7.0 [H+]= 1x10-7 pH= 8.5 [H+]= 3.2x10-9
  12. 12. Calculate [H+] given pH pH = 7.0 [H+]= 1x10-7 pH= 8.5 [H+]= 3.2x10-9 = between 1x10-9 and 1x10-8 1. Enter pH value in calculator 2. Press the +/- key 3. Press the 10x key OR in the reverse order depending on your calculator!
  13. 13. From pH0 to pH14 the H+ concentration decreases 100,000,000,000,000 times!!
  14. 14. Relationship between [H+] and [OH-] [H3O+][OH-] = 1.0 x 10-14 ALWAYS!!
  15. 15. Relationship between [H+] and [OH-] [H3O+][OH-] = 1.0 x 10-14 ALWAYS!! If [H+] = 1.0 x 10-5 then, [OH-] = 1.0x10-14/ 1.0x10-5 = 1 x 10-9 SUBTRACT THE EXPONENTS!
  16. 16. Relationship between [H+] and [OH-] [H3O+][OH-] = 1.0 x 10-14 If [H+] = 5.0 x 10-4 then, [OH-] = 1.0x10-14/ 5.0x10-4 = 2 x 10-11
  17. 17. Acidic = more H+ than OH- Basic = more OH- than H+ There is always some of each ion in water no matter what the pH
  18. 18. Relationship between pH and pOH pOH = -log[OH-] pH + pOH = 14 Always!!
  19. 19. pH pH + pOH = 14 pOH pH = pOH = -log[H+] -log[OH-] [H+] [H+][OH-]=1x10-14 [OH-]
  20. 20. pH pH + pOH = 14 pOH [H+] = [OH-]= 10-pH 10-pOH [H+] [H+][OH-]=1x10-14 [OH-]
  21. 21. Calculate pH ↔ pOH What is the pH of a solution with pOH = 13? Is the solution acidic or basic? What is the pOH of a solution with pH = 8? Is the solution acidic or basic? What are the concentrations of H+ and OH-?
  22. 22. Calculate pH ↔ pOH What is the pH of a solution with pOH = 13? Is the solution acidic or basic? pH= 1, acidic What is the pOH of a solution with pH = 8? Is the solution acidic or basic? pOH = 6, basic What are the concentrations of H+ and OH-? [H+] = 1.0x10-1, [OH-] = 1.0x10-13 [H+] = 1.0x10-8, [OH-] = 1.0x10-6

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