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Acids And Bases!

Acids And Bases!. chapter 14. Are in citrus fruits. The Nature of Acids and Bases. Arrhenius Definition Bronsted-Lowry Definition HA + B  A - + HB + Conjugate acid-base pair. Equilibrium Expressions.

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Acids And Bases!

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  1. Acids And Bases! chapter 14 Are in citrus fruits

  2. The Nature of Acids and Bases • Arrhenius Definition • Bronsted-Lowry Definition HA + B  A- + HB+ Conjugate acid-base pair

  3. Equilibrium Expressions • Acid dissociation constant is for the equilibrium that exists as an acid spontaneously dissociates. • Works the same as the other equilibrium expressions we’ve been writing.

  4. Acid Strength

  5. Types of acids • Diprotic Acids- two hydrogen atoms, dissociate with different strengths. • Oxyacids- H is attached to an oxygen. • Organic Acids- contain a carboxyl group. • Hydrohalic Acids- H attached to a halogen.

  6. Autoionization of Water • Water is amphoteric (properties of acid and base) Do Now Write the equilibrium expression for the autoionization of water. Kw = 1.0 x 10^-14

  7. The pH Scale • pH = -log[H+] • Related by exponents of 10. As [H+] increases, the pH will decreases. log Kw = log [H+] + log [OH-] pKw = pH + pOH 14 = pH + pOH The number of S.F. in the concentration value equals the number of decimal places in the pH value.

  8. Try Me Problems!! • Calculate the pH or pOH as required for each of the following solutions at 25oC, and state whether the solution is neutral, acidic, or basic. a) 1.0 x 10-5 M OH- b) 1.0 x 10-7 M OH- c) 1.0 M H+

  9. More Try Me! • Calcualte pH and pOH for each of the solutions from the problem before.

  10. Even More Try Me! • The pH of a sample of human blood was measured to be 7.41 at 25oC. Calculate the pOH, [H+], and [OH-] for the sample.

  11. Acid Strength Matters • Identify the MAJOR SPECIES present in your sample. • Determine if the autoionization of water will impact the concentration of [H+] or not (compare concentrations)

  12. Strong Acid Example Lets pretend I have 1.0 M HCl. major species: H+ , Cl-, H2O H+ from HCl will be 1.0 M H+ from H2O will be 1.0 x 10-7 M H+ from H2O is negligible. We can now base our calculations on the H+ values from our major species.

  13. In the Event of a Weak Acid… • Write out major species. • Determine if H20’s H+ are significant. • Write Ka for dominating species • Use an ICE chart

  14. Weak Acid Example Lets pretend I have 1.0 M HF, solve for [H+] major species: HF, H2O HF H+ + F- Ka = 7.2 x 10-4 H2O H+ + OH- Kw= 1.0 x 10-14 Dominating source of H+: HF

  15. ICE it up! HF H+ + F- I 1.0 0 0 C -x +x +x E 1-x x x Plug into Ka expression, BUT DO NOT SOLVE YET

  16. 5% rule • If x is small, cross out subtracted/added x’s • How small? 5% of original concentration. • Similarly, percent dissociation/ionization has formula:

  17. Try Me! • Calculate the pH of a solution that contains 1.0 M HCN (Ka = 6.2 x 10-10) and 5.0 M HNO2 (Ka = 4.0 x 10-4). Also calculate the concentration of cyanide ion (CN-) in this solution at equilibrium.

  18. Try Me Trickier! Lactic acid (HC3H5O3) is a waste product that accumulates in muscle tissue during exertion, leading to pain and fatigue. In a 0.10 M aqueous solution, lactic acid is 3.7 % dissociated. Calculate Ka for the acid.

  19. Bases • Strong bases have/cause complete ionization, just like acids. • KOH and NaOH are the most common group I soluble strong bases • Group II hydroxides are insoluble strong bases • Not all bases need to have OH- (Brønsted Lowry) H3CNH2(aq) + H2O(l) H3CNH3+(aq) + OH-(aq)

  20. Common Base Structures Ammonia Methylamine Dimethylamine Pyridine Ethylamine Ephedrine

  21. Useful Application • Amines can form soluble acid salts Pseudoephedrine + HCl ↔ pseudophedrineHCl

  22. Strong Base Try Me Calculate the pH of a 5.0 x 10-2 M NaOH solution.

  23. Weak Base Try Me Calculate the pH of a 15 M solution of ammonia (Kb = 1.8 x 10-5)

  24. Polyprotic Acids • Dissociate stepwise • For weak acids, Ka1 > Ka2 > Ka3 • Sulfuric acid is a freak because it is strong for hydrogen 1 and a weak acid for hydrogen 2. Only impacts normal process if we are using dilute solutions.

  25. Try ME! Concentrated H2SO4 Calculate the pH of a 1.0 M solution of H2SO4.

  26. Try Me 2! Dilute H2SO4 • Calculate the pH of 1.0 x 10-2 M H2SO4

  27. Regular Type Polyprotics Calculate the pH, and the concentration of each ion formed by the complete dissociation of hydrogen in a 5.0 M solution of phosphoric acid.

  28. Onceupon a time there was a salt… • What is a salt? • What power does it have in solution?

  29. salt of a strong acid and a strong base salt of a weak acid and a strong base salt of a strong acid and the C.A. of a weak base salt of the C.B. of a weak acid and the C.A. of a weak base salt with a highly charged metal cation varies Solution is Basic Solution is Neutral Solution is Acidic

  30. Try This On! Calculate the pH of a 0.10 M NH4Cl solution, given that Kb for NH3 is 1.8 x 10-5

  31. Structural Effects • Hydrohalic Acids • Bond Strength • Bond Polarity • Oxyacids • Number of Oxygen atoms H-F H-Br H-I H-Cl

  32. OXIDES Covalent oxides in water form acids • CO2 + H2O  H2CO3 • Ionic oxides in water form bases • K2O + H2O  2KOH H-O-X If X has low EN, OH stays together and oxide acts as a base. If X has high EN, the oxide will act as acid

  33. Lewis Definition • Lewis Acids • Accepts e- pair • Lewis Bases • Dontates e- pair

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