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Bases

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Bases

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  1. Acids and Bases

  2. Properties of Acids • pH < 7.0 • Electrolytes • Taste Sour • React with bases to form H2O + Salt • React with metals to form H2(g) and salt Table J

  3. Properties of Bases • pH > 7.0 • Electrolytes • Taste Bitter • React with acids to form H2O + Salt • Slippery, soapy feeling

  4. What is an acid? Arrhenius  gives off an H+ and forms H3O+ - increases the H+ when dissolved in water Bronsted  proton [H+] donor (loses an H+) HCl  H+ + H2O  H+ + Cl- H3O+

  5. What is a base? Arrhenius  gives off an OH- NaOH + HCl H2O and NaCl Bronsted  proton [H+] acceptor (gains an H+) NaOH  Ca(OH)2  Na+ + OH- Ca+2 + OH- 2

  6. Universal Indicator pH Indicators Chemicals which change colors when they are put into acids or bases. These indicators change colors in response the [H+]. Table M

  7. pH Indicators

  8. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base Neutralization reactions - Products are always water and salt • Perform titrations to determine an unknown volume or concentration of an acid/base • ENDPOINT = when indicator changes color • Moles of H+ = Moles of OH- MAVA = MBVB

  9. Conjugate Pairs

  10. Conjugate Acid-Base Pairs Strong acids have weak conjugate bases Weak acids have strong conjugate bases HCl + KOH  HOH + KCl acid base conj. acid conj. base  H2CO3 + 2NaCl Na2CO3 + 2HCl base acid conj. acid conj. base  HSO4- + H3O+ H2O + H2SO4 conj. acid acid base conj. base

  11. Practice Problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq) conjugate base conjugate acid acid base conjugate acid-base pairs OH–(aq) + HCO3–(aq)  CO32–(aq) + H2O(l) acid conjugate base conjugate acid base conjugate acid-base pairs

  12. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base Titration problems If 20.0ml of a 0.50M HCl solution is needed to neutralize 65.0ml of a NaOH solution. What was the concentration of the base? MAVA = MBVB (0.5M)(20.0ml) = MB(65.0ml) MB= 0.154M

  13. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base Titration problems 43.0ml of HCl was titrated with 32.0 ml of 0.100 M NaOH. What is the molarity of the hydrochloric acid solution? MAVA = MBVB MA(43.0ml)=(0.100M)(32.0ml) MA= 0.0744 M

  14. Bell Ringer Information related to an experiment is listed below: H2SO4 + 2KOH  K2SO4 + 2H2O Results Based on the above results, what is the concentration of H2SO4?

  15. Setup for titrating an acid with a base

  16. Titration #1 Lab

  17. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base Titration problems Calculate the molarity of an acetic acid solution if 34.57 mL of this solution are needed to neutralize 2.519 cL of 0.1025 M sodium hydroxide MAVA = MBVB (MA)(34.57ml) = (0.1025M)(25.19ml) MA= 0.07469M

  18. pH of Common Substances

  19. What is pH? • a way to measure the concentration of H+ ions (H3O+) in a solution • concentration of H+ = [H+] pH = -log[H+] If [H+] = 1 x 10-4, then pH = 4 If [H+] = 1 x 10-13, then pH = 13 If [H3O+] = 1 x 10-7, then pH = 7

  20. Practice pH As the pH of a solution is changed from 3 to 6, how does the concentration of hydronium ions change? What is the pH of a 0.00001 molar HCl solution? If the pH of your pool is 6, what is the concentration of hydronium ions in solution? An aqueous solution that a [H+] of 1.0 x 10-8 mole per liter has a pH of?

  21. pH What is the difference in [H+] in a pool that has a pH of 6, but in reality you want it to have a pH of 7? • Because it is a logarithmic scale, each one unit change in pH really represents a 10 fold change in [H+] • So going from a pH of 6 to 7 really represents a 10 fold decrease in the number of [H+]

  22. pH and pOH [H+][OH-] = 10-14 pH + pOH = 14 If [OH] = 10-8 M, what is the pH? Solution: • the OH = 8, so the pH must be 14 – 8 • So the pH = 6

  23. pH Scale

  24. Titration #2 Lab

  25. Bell Ringer Solution A has a pH of 1 and solution Z has a pH of 5. How many times greater is the hydronium ion concentration in solution A?

  26. Quiz: A & B #2

  27. pH Scale

  28. Buffers • A compound that does not allow the pH to change even if an acid or base is added to the system • They have the ability to absorb/release H+ which will keep the pH relatively constant • Good buffers are amphiprotic substances • Amphiprotic – something that can act as an acid and a base

  29. Brooktrout Lake Buffers • Blood pH • Adirondack lakes "Treat the earth well: it was not given to you by your parents, it was loaned to you by your children. We do not inherit the Earth from our Ancestors, we borrow it from our Children."

  30. Effects of Acid Rain on Marble(marble is calcium carbonate) George Washington: BEFORE acid rain George Washington: AFTER acid rain

  31. pH Indicators

  32. Bell Ringer The pH of a lake is 8.0. Over a 10 year period, the pH of the water becomes 1000x more acidic. • Name an ion that has increased in the water over the 10 years? • What is the pH now? • If you were to use bromothymol blue to test the pH, what color would it be? [Use R.T.]

  33. Wkst – p.84 and 85

  34. Bronsted-Lowry Acids and Bases wkst 1. H2O + H2O  H3O+ + OH- 2. H2SO4 + OH- HSO4- + H2O 3. HSO4- + H2O  SO4-2 + H3O+ 4. OH- + H3O+ H2O + H2O 5. NH3 + H2O  NH4+ + OH-

  35. Conjugate Acid-Base Pairs wkst H2PO4- H3PO4 ↔ H+ + H2PO4- HF HF ↔ H+ + F- HNO3 HNO3 ↔ H+ + NO3- HPO4-2 H2PO4- ↔ H+ + HPO4-2 OH- H2O ↔ H+ + OH- HSO4- HSO4-↔ H+ + SO4-2 PO4-3 HPO4-2 ↔ H+ + PO4-3 NH3 NH4+4 ↔ H+ + NH3 H3O+ H3O+ ↔ H+ + H2O

  36. Topic 10 Regents Questions PART C 36. Reduces error, increases reliability 37. Ca(OH)2 + H2SO4 CaSO4 + 2H2O 38. pH= 6.0 39. 0.33 M 40. HCl – 9.50 ml NaOH – 3.80 ml 41. 0.25 mL 42. Methyl orange, brom blue, thymol blue 43. Between 4.4 and 5.5 44. Yellow • A, C, D • D • Presence of H+ ions • C • C • (10.01mL)(0.100M)= MB(5.01ml) • 0.200 M • 32. 7 • 33. Colorless to pink. • 34. 0.21 M • 35. 0.97 M

  37. Topic 10 Regents Questions • 4 • 3 • 4 • 3 • 1 • 1 • 1 • 4 • 2 • 1 • 3 • 1 • 2 • 4 PART A PART B • 1 • 3 • 2 • 4 • 2 • 3 • 1 • 2 • 1 • 4 • 2

  38. Bell Ringer In a lab there were three flasks, one filled with methanol, another had NaOH, and the third HCl. ID these liquids. • A student concluded that bottle C contained HCl. Identify one way that supports this finding. • Explain in terms of pH, why methyl orange was the same for all three liquids.

  39. Bell Ringer What is the volume of 1.00 mole of any gas at STP? Hint: Lab