1. Chapter 16 Acids and Bases

2. Characteristics Acids: Sour taste –Lemons, Oranges (citric acid) Bases: Slippery, bitter taste –Soaps Change the color of dyes

3. Characteristics Add acid to water makes water acidic Add base to water makes it more basic Add acid to base neutralizes NaOH + HCl  NaCl + H 2 O

4. Arrhenius Acids –Donate H + –Increase [H + ] Bases –Donate OH - –Increase [OH - ]

5. Bronsted/Lowry Acids –Transfer proton to another substance Bases –Accept protons from another substance

6. Water as a Bronsted/Lowry H 2 O  H + + OH - H + + H 2 O  H 3 O + Hydronium can bond to many other water molecules

7. Water and Hydronium H 2 O + HCl  H 3 O + + Cl - Where water is a base HCl is 100% ionized Hydronium is the conjugate acid Chloride is the conjugate base

8. Ammonia as a base HCl +NH 3  NH 4 + + Cl - H 2 O +NH 3  NH 4 + + OH - An acid and a base always work together to transfer protons.

9. Amphoteric Species A compound that can act as both an acid and a base under different conditions. Water –Base with HCl –Acid with NH 3

10. Conjugate acids and bases Every acid/base reaction has –Acid –Base –Conjugate acid –Conjugate base –H 2 O +NH 3  NH 4 + OH -

11. Practice What are the conjugate bases of the following acids? HClO 4 H 2 S PH 4 +

12. Practice What are the conjugate acids of the following bases?  CN -  SO 2 -2  HCO 3 -

13. Strong Acids 100% ionized HCl, H 2 SO 4, HNO 3 HCl  H + + Cl - –Reaction is not reversible –Cl - is a weak base and does not accept protons

14. Seven Strong Acids HCl HBr HI HClO 4, HClO 3 HNO 3 H 2 SO 4

15. Strong Bases 100% ionized Group 1 hydroxides, heavy Group 2 NaOH + H 2 O  NaH 2 O + + OH - –Conjugate acid is weak CH 3 - is a VERY strong base –No acidity and takes proton from water

16. Weak Acids Slightly dissociated CH 3 COOH + H 2 O  CH 3 COO - + H 3 O + Scale on page 598, fig 16.4

17. Generally HX + H 2 O  H 3 O + + X - If HX is stronger than water, rxn right If HX is weaker than water, rxn left Equilibrium favors transfer of proton from stronger acid to stronger base

18. Practice NH 4 + + OH -  NH 3 + H 2 O –Does the equilibrium lie to the right or left? –Why

19. Autoionization of water H 2 O + H 2 O  H 3 O + + OH - This is a very fast reaction Only about 1 out of 10 9 water molecules are dissociated at any time

20. Generally Shown as: H 2 O  H + + OH -

21. Ion Product H 2 O + H 2 O  H 3 O + + OH - K c = [H + ] [OH - ] [H 2 O] But water is a constant so…

22. MEMORIZE THIS! K c [H 2 O] = [H + ][OH - ] K w = [H + ][OH - ] = 1 x 10 -14 At equilibrium [H + ]=[OH - ]= 1 x 10 -7

23. Practice Remember: at equilibrium [H + ]=[OH - ]= 1 x 10 -7 Identify the following as acid or base [H + ] = 1 E –5 [OH - ] = 3.2 E –9 [H + ] = 7.1 E –8 [OH - ] = 4.6 E –3

24. pH scale Cumbersome to always use exponents Use logarithmic scale to deal with exponent MEMORIZE: pH = -log [H + ]

25. So… If [H + ] = 1E -7 then –log[1E -7 ] = 7 Therefore… the pH of a neutral solution is 7 –(equal amounts of H + and OH - )

26. Calculations involving pH If given [OH - ] there are two methods to get pH 1. Use K w = [H + ][OH - ] = 1 x 10 -14 to solve for [H + ] Then use pH = -log[H + ]

27. Calculations involving pH What is pH if [OH - ] = 3.2 E -5 ? 2. pOH = - log[OH - ] –If K w = 1E -14, then pK w = pH + pOH = pK w

28. The pH scale If the pH < 7, the solution is acidic If the pH > 7, the solution is basic If the pH = 7, the solution is neutral See fig 16.5 p. 602

29. Practice Calculate the pH of lemon juice that has a [H + ] = 3.8 E -4 M

30. How do you undo a logarithm? If pH = -log [H + ] Then [H + ] = 10 -pH

31. Practice What is the [H + ] of a solution that has a pH of 4.2 9.47 What is the [OH - ] of each solution?

32. Practice What is the pH of 0.005 M HCl? What is the pH of 0.024 M Ca(OH) 2 What is [HNO 3 ] if pH = 2.45

33. Quiz 1.What is the pH of a solution that has [OH - ] = 4.33 x 10 –6 M? 2.What is the [H + ] of a solution that has a pH of 3.75 3.What is the pOH of a solution that has a [H + ] = 7.244 x 10 -3 4.Identify all of the above as either acid/base

34. Weak Acids… Write the acid ionization expression for HCHO 2, formic acid, dissolving in water. This is an equilibrium expression. This gets the designation K a

35. HCHO 2  H + + CHO 2 - A student prepared a 0.10 M solution of formic acid and measured its pH. At 25 o C, it was found to be 2.38. Calculate K a ICE Box

36. Niacin… A 0.20 M solution of niacin has a pH of 3.26. what is the K a for niacin? ICE Box

37. Practice Calculate the percentage of HF molecules ionized in: 1.A 0.10 M HF solution 2.A 0.01 M HF solution

38. Weak Bases Substances that react with water to form a cation and OH - NH 3(aq) + HOH (l)  NH 4 + (aq) + OH - (aq) Write the K b expression.

39. Types of Weak Bases Amines: compounds that have a NH 2 component –i.e. methylamine CH 3 NH 2 Anions of weak acids –i.e. ClO 2 - from chlorous acid –Dissolve NaClO 2 in water…

40. K a and K b Write the appropriate K expression for NH 4 + (aq)  NH 3(aq) + H + (aq) Write the appropriate K expression for NH 3(aq) + HOH (l)  NH 4 + (aq) + OH - (aq)

41. Hess’ Law Add the previous equations together… what do you get? When two reactions are added to give a third reaction, the equilibrium constant for the third reaction is equal to the product of the equilibrium constants for the two added reactions.

42. Then… The product of the acid-dissociation constant, K a, for an acid and the base- dissociation constant, K b for its conjugate base is the ion-product constant for water. So… K a x K b = K w

43. Application… K a x K b = K w = 1.00 E -14 If you know one, you can solve the other. Can be modified… take the ‘p’ of each and you get… pK a + pK b = pK w = 14.00

44. Practice What is the value for Ka for NH 4 + ? For NH 3, Kb= 1.8 E -5 The equation is: NH 3(aq) + HOH (l)  NH 4 + (aq) + OH - (aq)

45. Salts Ions can exhibit acid/base behavior when they react with water Only anions/cations of weak acids/bases

46. Basic Solutions Generally, anions, X-, from weak acids behave as follows in water, X - + HOH  HX + OH -

47. Application/Practice Predict whether NaHPO 4 will form a basic or acidic solution when it dissolves in water. Write two equations… Find K a and K b

48. Rules 1.Salts derived from a strong base and a strong acid give pH = 7. Neither the anion or cation react with water. 2.Salts derived from a strong base and a weak acid. Anion from acid hydrolyzes in water. pH above 7 1.i.e. NaClO 2.Ba(C 2 H 3 O 2 ) 2

49. Rules 3.Salts derived from a weak base and a strong acid. The cation is a strong conjugate acid. pH below 7 i.e. NH 4 Cl i.e. Al(NO 3 ) 3

50. Rules 4. Salts derived from a weak base and a weak acid. Both cation and anion hydrolyze. pH depends on the value of K a or K b. i.e. NH 4 CN – find appropriate K a and K b and compare.

51. Practice Will the following salts give acidic, basic, or neutral solutions? 1.NaNO 3 2.KBrO 3.CH 3 NH 3 Cl 4.NH 4 NO 3