The Chemistry of Acids and Bases

1. The Chemistry of Acids and Bases

2. What is an Acid?

3. Acid and Bases

4. Acid and Bases

5. Acid and Bases

6. Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Bases Have a bitter taste. Feel slippery. Many soaps contain bases.

8. Acids in Chemistry • An acid is something that when dissolved in water (broken apart) yields hydrogen cations.

9. Some Properties of Acids • Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) • Taste sour • Corrode metals • Electrolytes • React with bases to form a salt and water • pH is less than 7 • Turns blue litmus paper to red “Blue to Red A-CID”

10. Acid Nomenclature Review Binary  Ternary An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

11. Acid Nomenclature Flowchart

12. Examples • HCl (Chloride ends in –ide, therefore changed to –ic and hydro added in front) • Hydrochloric Acid • H2SO3 (SO3= Sulfite) therefore changed to –ous followed by the word acid • Sulfurous Acid • HNO3 (NO3 =Nitrate) therefore changed to –ic followed by the word acid • Nitric Acid

13. Acid Nomenclature Review • HBr (aq) • H2CO3 • H2SO3  hydrobromic acid  carbonic acid  sulfurous acid

14. Name ‘Em! • HI (aq) • HCl (aq) • H2SO3 • HNO3 • HIO4

15. Some Properties of Bases • Produce OH- ions in water • Taste bitter, chalky • Are electrolytes • Feel soapy, slippery • React with acids to form salts and water • pH greater than 7 • Turns red litmus paper to blue “Basic Blue”

16. Some Common Bases NaOH sodium hydroxide lye KOH potassium hydroxide liquid soap Ba(OH)2 barium hydroxide stabilizer for plastics Mg(OH)2 magnesium hydroxide “MOM” Milk of magnesia Al(OH)3 aluminum hydroxide Maalox (antacid)

17. Strong Acids and Bases • Acids are classified as strong or weak by how much they ionize (break apart) in water • Strong acids dissociate 100% • Strong Bases dissociate 100%

18. Strong Acids • Hydrochloric acid:  HCl Hydrobromic acid:  HBr Hydroiodic acid:  HISulfuric acid:  H2SO4 Nitric acid:  HNO3Phosphoric Acid: H3PO4

19. Strong Bases • Group 1 and Group 2 Hydroxides • Lithium hydroxide:  LiOH Sodium hydroxide:  NaOH Potassium hydroxide:  KOH Rubidium hydroxide:  RbOH Calcium hydroxide:  Ca(OH)2Strontium hydroxide:  Sr(OH)2Barium hydroxide:  Ba(OH)2

20. Acid Base Theories • Monoprotic Acids: 1 ionizable hydrogen • Diprotic Acids: 2 ionizable hydrogens • Triprotic Acids: 3 ionizable hydrogens

21. Ionizable Hydrogens • Only hydrogens in very polar bonds, that is those bonding with very electronegative elements are ionizable

22. Examples • HCl • Ethanoic Acid • CH3COOH • Methane • CH4

23. Acid/Base definitions • Definition #1: Arrhenius (traditional) Acids – produce H+ ions (or hydronium ions H3O+) Bases – produce OH- ions (problem: some bases don’t have hydroxide ions!)

24. Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water

25. Acid/Base Definitions • Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

26. ACID-BASE THEORIES The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

27. Acids & Base Definitions Definition #3 – Lewis Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair

28. Lewis Acids & Bases Formation of hydronium ion is also an excellent example. • Electron pair of the new O-H bond originates on the Lewis base.

29. Lewis Acid/Base Reaction

30. The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion.Under 7 = acid 7 = neutralOver 7 = base

31. Self-Ionization • Process which water molecules produce ions is called self-ionization • H2O (l) H+ + OH- • In water or aqueous solution, all H+ ions exist as (H3O+)

32. [H+] and [OH-] • Any solution in which [H+] and [OH-] concentrations are equal is called a neutral solution • If [H+] increases, [OH-] decreases, and the opposite

33. Acidic and Basic Solutions • Acidic solutions have more [H+] than, [OH-] • Basic solutions, also called alkaline solutions, have more [OH-] than [H+]

34. pH • Because expressing hydrogen ion concentration in molarity is troublesome, the pH system was created • pH = - log[H+] • pH expressed between 0 & 14, 0 being the most acidic, 14 the most basic, and 7 being neutral

35. Neutral Solutions • In a neutral solution [H+] = 1 x 10-7

36. pOH • pOH = - log[OH-] • 14- pH= pOH

37. pH of Common Substances

38. pH [H+] [OH-] pOH

39. Weak Bases

40. Ionization Constants for Acids/Bases Conjugate Bases Acids Increase strength Increase strength

41. Relation of Ka, Kb, [H3O+] and pH

42. pH testing • There are several ways to test pH • Blue litmus paper (red = acid) • Red litmus paper (blue = basic) • pH paper (multi-colored) • pH meter (7 is neutral, <7 acid, >7 base) • Universal indicator (multi-colored) • Indicators like phenolphthalein • Natural indicators like red cabbage, radishes

43. Paper testing • Paper tests like litmus paper and pH paper • Put a stirring rod into the solution and stir. • Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper • Read and record the color change. Note what the color indicates. • You should only use a small portion of the paper. You can use one piece of paper for several tests.

44. pH paper

45. pH meter • Tests the voltage of the electrolyte • Converts the voltage to pH • Very cheap, accurate • Must be calibrated with a buffer solution

46. pH indicators • Indicators are dyes that can be added that will change color in the presence of an acid or base. • Some indicators only work in a specific range of pH • Once the drops are added, the sample is ruined • Some dyes are natural, like radish skin or red cabbage