1. Acids and Bases The concept of acidic and basic solutions is perhaps one of the most important topics in chemistry. Acids and bases affect the properties of foods, biochemical reactions, pharmaceuticals, and industrial materials.

2. Acids and Bases Properties of Acids Sour or tart taste. Corrosive (deteriorate). Electrolytes Electrolytes are able to conduct an electrical current because of the presence of ions in aqueous solutions.

3. Acids and Bases Properties of Acids (cont.) Will react with most metals to form hydrogen gas. Some acids are ‘stronger’ than others All acids contain a hydrogen that they can give away.

4. Acids and Bases Properties of Bases Bitter tasting Slippery Caustic – They will degrade biological tissue. Chemical burns from strong bases are nasty. Bases form the hydroxide ion (OH -1 ) in water.

5. Acids and Bases Arrhenius Acids Svante Arrhenius (1900) defined an acid. Acids are hydrogen containing compounds that yield a hydrogen ion (H + ) in water. An Arrhenius acid donate an H + ion.

6. Acids and Bases Arrhenius Acids HCl (s)  H + (aq) + Cl - (aq) H 2 SO 4(s)  H 2 O (l) 

7. Acids and Bases Arrhenius Acids Acids that have one hydrogen ion to donate are called monoprotic. Acids that have 2 hydrogen ions to donate are called diprotic. Acids that have 3 hydrogen ions to donate are called ____protic.

8. Acids and Bases Arrhenius Bases Compounds that produce the hydroxide ion(s) (OH -1 ) in water are called Arrhenius Bases. NaOH (s) 

9. Acids and Bases Arrhenius Acids and Bases Problem with the Arrhenius definition; Some bases can form OH- ions in solution but not have an OH- ion in the chemical formula. NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

10. Acids and Bases Bronsted-Lowry Acids and Bases A better definition of an acid and a base Bronsted-Lowry Acid – A molecule that donates an H + to another molecule. Bronsted-Lowry Base – A molecule that accepts an H + from the B-L acid. Identify the Bronsted-Lowry acid and base; NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

11. Acids and Bases Bronsted-Lowry Acids and Bases Conjugate Acid – becomes the H+ donor in the reverse reaction. Conjugate Base – becomes the H+ acceptor in the reverse reaction. Identify the BL acid, base, conjugate acid and conjugate base; HClO 2(aq) + H 2 O (l)  H 3 O +1 (aq) + ClO 2 - (aq)

12. Acids and Bases The pH Scale – Measures the concentration of H+ ion in an aqueous solution.

13. Acids and Bases The pH Scale Remember that a water molecules ionizes; H 2 O (l)  H + (aq) + OH - (aq) In pure water, the concentration of H + and OH - each is 1.0 x 10 -7 M

14. Acids and Bases The pH Scale H 2 O (l)  H + (aq) + OH - (aq) Therefore, the product of [H + ] and [OH - ] must be equal to 1.0 x 10 -14 M 2. An aqueous solution will always have the concentration of H + and OH - equal to 1.0x10 -14 M 2.

15. Acids and Bases The pH Scale H 2 O (l)  H + (aq) + OH - (aq) K eq = [H + ] x [OH - ] K w = [1.0x10 -7 ] x [1.0x10 -7 ] = 1.0x10 -14 K w is called the autoionization constant for water.

16. Acids and Bases The pH Scale K eq = [H + ] x [OH - ] [1.0x10 -7 ] x [1.0x10 -7 ] = 1.0x10 -14 If the addition of an acid makes the [H + ] increase, then the [OH - ] will decrease. If the addition of a base makes the [OH - ] increase, the [H + ] will decrease.

17. Acids and Bases The pH Scale Calculate the [H + ] if 0.05 moles of HCl is added to 1.0 L of water.

18. Acids and Bases The pH Scale pH is a measure of the concentration of H +. pH = -log[H + ]

19. Acids and Bases The pH Scale What is the pH of an aqueous solution where [H + ] = 1.0 x 10 -7 ? What is the pH of an aqueous solution where [H + ] = 1.0 x 10 -2 ?

20. Acids and Bases The pH Scale What is the pH of an aqueous solution where [H + ] = 2.7 x 10 -1 ? What is the pH of an aqueous solution where [H + ] = 8.0 x 10 -12 ?

21. Acids and Bases The pH Scale Since K w = 1 x 10 -14 = [H + ] x [OH - ] 14 = pH + pOH

22. Acids and Bases The pH Scale Calculate the pOH of an aqueous solution that has an [H+] = 1.0 x 10 9.

23. Acids and Bases The pH Scale Calculate the [H + ] of an acid with a pH of 4. Calculate the [H+] of a base with a pH of 10.8.

24. Acids and Bases The pH Scale Calculate the [OH - ] of an acid with a pH of 2. Calculate the [OH-] of a base with a pH of 12.9.

25. Acids and Bases Strong Versus Weak Acids What makes some acids ‘strong’ and some ‘weak’?

26. Acids and Bases Strong Versus Weak Acids We can quantify the relative strength of an acid by using it’s equilibrium expression (K a ). K a = [products] x = [H+] x [conj. base] [reactants] y [acid]

27. Acids and Bases Strong Versus Weak Acids Write the K a expression for HCl. K a =

28. Acids and Bases Strong Versus Weak Acids Write the K a expression for H 3 PO 4. K a =

29. Acids and Bases Strong Versus Weak Acids As the [H + ] increases, K a increases. Therefore the greater the value of K a, the more [H + ] present, the stronger the acid.

30. Acids and Bases Weak Acids The pH of a 1.0 M solution of formic acid, HCOOH, is 2.38. Calculate the K a for formic acid.

31. Acids and Bases Weak Acids Calculate the K a of a 0.220 M solution of H 3 AsO 4 that has a pH of 1.50.

32. Acids and Bases Weak Acids Calculate the K a of a 0.0400 M solution of HClO 2 that has a pH of 1.80.

33. Acids and Bases Weak Acids Calculate the pH of a 8.6 x 10 -3 M solution of H 3 PO 4. K a of H 3 PO 4 is 1.4 x 10 -3.

34. Acids and Bases Salt Hydrolysis Sometimes an ion from a salt can make an aqueous solution acidic or basic. What happens when sodium bicarbonate dissolves in water?

35. Acids and Bases Salt Hydrolysis NaHCO 3(aq)  Na + (aq) + HCO3 - (aq) HCO 3 - (aq) + H 2 O (l)  H 2 CO 3(aq) + OH- (aq) Now there will more OH - than H + in the solution making it basic.

36. Acids and Bases Salt Hydrolysis Will a solution of ammonium chloride, NH 4 Cl, be acidic or basic?

37. Acids and Bases Buffers A buffer is a solution that resists changes in pH when either an acid or a base is added. Buffers consist of either a weak acid with one of its salts, or a weak base with one of its salts.

38. Acids and Bases Buffers For example, if a solution is make by dissolving carbonic acid (weak acid) and sodium bicarbonate (salt of the acid) we get the following; H 2 CO 3(aq) + H 2 O (l)  H 3 O + (aq) + HCO 3 -1 (aq)

39. Acids and Bases Buffers H 2 CO 3(aq) + H 2 O (l)  H 3 O + (aq) + HCO 3 -1 (aq) If we add a base to this buffered solution, the H 3 O + will scoop it up. H 3 O + (aq) + OH - (aq)  2H 2 O (l)

40. Acids and Bases Buffers H 2 CO 3(aq) + H 2 O (l)  H 3 O + (aq) + HCO 3 -1 (aq) If we add an acid to this buffered solution, the HCO 3 -1 will scoop it up. H + (aq) + HCO 3 -1 (aq)  H 2 CO 3(aq)

41. Acids and Bases Buffers Write the chemical reaction for the phosphoric acid – dihydrogen phosphate buffer reaction.

42. Acids and Bases Neutralization Reactions o Occurs when an equal number of H + ions and OH - ions react. HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) o The products of a neutralization reaction are always a salt and water.

43. Acids and Bases Neutralization Reactions KOH (aq) + HNO 3(aq)  Ca(OH) 2(aq) + HClO 3(aq)  H 2 SO 4(aq) + LiOH (aq) 

44. Acids and Bases Titrations – Reacting an acid with a base to a specific pH.

45. Acids and Bases Titrations o The purpose of a titration is to determine the concentration of either the acid or the base being titrated. o Usually, the buret contains a known concentration of base while the acid is of an unknown concentration.

46. Acids and Bases Performing a Titration 1.Add a desired amount of the acid into the flask. 2.Load the buret with the base of a known concentration.

47. Acids and Bases Performing a Titration 3.Record the initial volume of the base in the buret. A buret can give a volume reading to 0.01 mL. 4.Add a few drops of the indicator.

48. Acids and Bases Performing a Titration 5. Slowly dispense the base into the acid. Your goal is to change the color of the acid from clear to pink with the addtion of one drop of the base.

49. Acids and Bases Titrations o After the titration is completed, we use the equation M A V A = M B V B to determine the concentration of the acid. M A = Concentration of Acid M B = Concentration of Base V A = Volume of Acid V B = Volume of Base

50. Acids and Bases Titrations o Calculate the concentration of 25.0 mL of an HCl solution that was titrated with 0.25 M NaOH. The initial volume in the buret read 3.50 mL and the final volume read 18.20 mL after the titration was completed.