Bellringer …

1. Bellringer… • As you come in grab a Ch. 14 Reading Guide and complete using your Zumdahl textbook.

2. Acids and Bases AP Chemistry

3. Acids • Acids • Properties • Sour taste. • React with metals to form a salt & hydrogen gas. • Reacts with blue litmus to turn it red. • Electrolytes. • Arrhenius Definition of an acid: acids are substances that release H+ ions in solution. • (When H+ attaches to H2O it forms H3O+, the hydronium ion.)

4. Acids • Dissociation of Acids • Strong acids dissociate 100% in solution. • HCl H+ + Cl- • Or HCl + H2O  H3O+ +Cl- • Weak acids dissociate partially and double arrows indicate this. • HC2H3O2 ↔ H+ + C2H3O2-

5. Write the dissociation equations for the following: 1. HClO4 2. HNO3 3. H2SO4 4. HBr 5. HF Note: Must memorize the strong acids and bases. • Acids: sulfuric, hydrochloric, nitric, perchloric • Bases: Group 1A metal hydroxides; Group 2A metal hydroxides

6. Bases • Characteristics • Slippery to touch. • Bitter taste. • Electrolytes • turns red litmus to blue • reacts with phenolphthalein to turn purple/pink. • Arrenhius definition: Bases are substances that produce OH­- ions in solution.

7. Bases 1. Strong bases dissociate 100%. • Ex) LiOH Li+ + OH- • Ca(OH)2 • Weak bases dissociate partially and this is indicated with a double arrow. Ammonia is the most famous weak base! • Ex) NH3 + H2O NH4+ + OH-

8. Bases • Neutralization: • Acid + Base  Salt + Water • HCl + KOH  • Complete these reactions • H2SO4 + NaOH • HCl + Ca(OH)2

9. Strong Acid and Strong Base • Net Ionic Equations • Strong Acid & Strong Base • You will always get H+ + OH-H2O • Ex) NaOH + HCl

10. Weak Acid and Strong Base • Weak Acid & Strong Base: remember not to dissociate the weak acid on the left side of the equation. • Ex) acetic acid + potassium hydroxide

11. Weak Base and Strong Acid Weak base & strong acid: remember not to dissociate the weak base on the left side of the equation. • Ex) Ammonia + hydrochloric acid

12. Weak Acid and Weak Base Weak acid & weak base: remember not to dissociate the weak acid or base on the left side of the equation. • Ex) acetic acid + ammonia

13. Practice problems • Beginning on Pg. 703 (Zumdahl) • 16-18, 29, 33-37

14. Bellringer… • Complete problems 16 and 29 beginning on pg. 703

15. Bronsted-Lowry model • An acid is a proton donor, a base is a proton accpetor. HA(aq) + H2O(l)  H3O+(aq) + A-(aq) AcidBaseconjugateconjugate acidbase Conjugate Base: Everything that remains of the acid molecule after a proton is lost Conjugate Acid: Formed when the proton is transferred to the base. Conjugate Acid-base pair: two substances related to each other by the donating and accepting of a single proton

16. Conjugate acid-base pair HA(aq) + H2O(l)  H3O+(aq) + A-(aq) AcidBaseconjugateconjugate acidbase • 2 acid-base pairs above • HA and A- • H2O and H3O+

17. Acid dissociation constant • HA(aq) + H2O (l)  H3O+(aq) + A-(aq) • Ka = = • Note: water is not included because, in dilute solution, the concentration of water is high, and changes so little it is assumed to be constant • Ex: Write out the equation to find Ka for the following: • HCl(aq) + H2O (l)  H3O+(aq) + Cl-(aq) • For strong acids such as HCl, the equilibrium lies so far to the right that [HCl] cannot be measured accurately, and an accurate calculation of Kais not possible

18. Acid Strength • Strong Acids • 1. Acids for which the equilibrium lies far to the right • a. Strong acids yield weak conjugate bases • 2. Common strong acids • a. sulfuric, hydrochloric, nitric, perchloric

19. Acid strength • Weak Acids • 1. Acids for which the equilibrium lies far to the left • a. Weak acids yield relatively strong conjugate bases • Acid Terminology • 1. Monoprotic - one acidic proton • 2. Diprotic - two acidic protons • 3. Triprotic - three acidic protons • 4. Oxyacids - acids in which the acidic proton is attached to an oxygen atom • 5. Organic acids - acids containing the mildly acidic carboxyl group • a. Generally weak acids • b. Equilibrium lies far to the left

20. Water as an acid and a base • 1. Water can act as an acid or as a base • a. Autoionization of water (Self-ionization) • 2. Ion-product constant, Kw(dissociation constant) • a. At 25°C, [H+] = [OH-] = 1.0 x 10-7 • b. Kw = [H+][OH-] = (1.0 x 10-7 mol/L)( 1.0 x 10-7 mol/L) • (1) Kw = 1.0 x 10-14mol2/L2 (units often dropped) • 3. Solution characteristics • a. Neutral solution, [H+] = [OH-] = 1.0 x 10-7 • b. Acid solution, [H+] > [OH-] • c. Basic solution, [H+] < [OH-]

21. Bellringer… • Complete problem numbers 35-37 on pg. 704

22. The ph scale • A. pH and pOH • 1. pH = -log[H+] • a. The number of decimal places in the log is equal to the number of significant figures in the original number • 2. pOH= -log[OH-] • 3. pH + pOH= 14

23. Solving acid-base problems • Please take time to read the advice at the end of this section (Page 665). It applies to far more than acid-base problems!

24. Calculating the pH of Strong Acid Solutions • What are the components of the solution? • 1. HA H+(aq) + A-(aq) • or • HA + H2O H3O+(aq) + A-(aq) • 2. H2O + H2O H3O+(aq) + OH-(aq) • or • H2OH+(aq) + OH-(aq) • Focus on the major species • 1. At high concentrations of strong acids, the autoionization of water is insignificant • 2. For strong acids, the assumption is that HA is completely ionized

25. example • Calculate the values of pH and pOH, and [OH-] in the following solutions • 0.020 M HCl • 0.00035 M Ba(OH)2

26. Strong acid v. weak acid Dissociation of Strong Acid Dissociation of Weak Acid

27. Calculating the pH of Weak Acid Solutions • Steps (from page 662) 1. List the major species in the solution 2. Choose the species that can produce H+, and write the balanced equations for the reactions producing H+ 3. Using the values of the equilibrium constants for the reactions you have written decide which equilibrium will dominate in producing H+ 4. Write the equilibrium expression for the dominant equilibrium 5. List the initial concentrations of the species participating in the dominant equilibrium 6. Define the change needed to achieve equilibrium; that is, define x 7. Write the equilibrium concentrations in terms of x 8. Substitute the equilibrium concentrations into the equilibrium expression 9. Solve for x the "easy" way; that is, by assuming that [HA]0 - x ≈ [HA]0 10. Use the 5% rule to verify whether the approximation is valid 11. Calculate [H+] and pH

28. example • A student planned an experiment that would use 0.10 M propionic acid, HC3H5O2, calculate the values of [H+] and pH for the solution. For propionic acid Ka = 1.4 x 10-5

29. Example (Base) • A solution of hydrazine, N2H4, has a concentration of 0.25 M. Kb = 1.7 x 10-6 • Calculate the pH and the percent ionization (dissociation).

30. Calculating ka and pka from ph • For any acid-base conjugate pair Ka x Kb = Kw • Also, • pKa + pKb = pKw = 14.00 Example: Lactic acid (HC3H5O3), which is present in sour milk, also give sauerkraut its tartness. In 0.100 M solution of lactic acid, the pH is 2.44 at 25oC. Calculate the Ka and pKa for lactic acid at this temp.

31. Practice problems • Beginning on pg. 704 • 39, 40, 43, 44 • 47, 51, 58, 59

32. Bellringer… • Complete problems 47 and 51 from pg. 705

33. Calculation ka from % dissociation • Refer to problem #65 on pg. 706

34. Calculating ph of a solution of 2 weak acids • Refer to problem #62 on pg. 706

35. Cont. example (62)

36. practice • Pg. 705-706 • 61, 66