Acids & Bases

1. Acids & Bases

2. Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

3. Definition of Electrolytes and Nonelectrolytes An electrolyte is: • A substance whose aqueous solution conducts • an electric current. A nonelectrolyte is: • A substance whose aqueous solution does not • conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes…

4. Electrolytes? • Pure water • Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure sodium chloride

5. Answers to Electrolytes ELECTROLYTES: NONELECTROLYTES: • Tap water (weak) • NaCl solution • HCl solution • Lactate solution (weak) • Pure water • Sugar solution • Ethanol solution • Pure NaCl But why do some compounds conduct electricity in solution while others do not…?

6. Electrolytes • Ionization • Formation of ions caused by a reaction between water molecules • Strong • Large amount of ionization occurs • Weak • Small amount of ionization occurs

7. Arrhenuis Definition • A substance that produces hydrogen ions (hydronium ions) as the only + ion when mixed with water • H+ = Hydrogen ion • H3O+ = Hydronium ion • The greater the # of H3O+ ions the stronger the acid and the stronger the electrolyte

8. Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids

9. Strong Acid Ionization

10. Weak Acid Ionization

11. Organic Acids Organic acids all contain the “carboxyl” group, sometimes several of them. The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

12. Examples of Organic Acids Citric acid in citrus fruit Malic acid in sour apples Deoxyribonucleic acid, DNA Amino acids, the building blocks of protein Lactic acid in sour milk and sore muscles Butyric acid in rancid butter

13. Properties of Acids • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids have a pH lower than 7 • Acids are proton (hydrogen ion, H+) donors • Acids react with active metals, produce H2 • Acids neutralize bases

14. Acids you SHOULD know: Strong Acids Weak Acids Sulfuric acid, H2SO4 Phosphoric acid, H3PO4 Hydrochloric acid, HCl Acetic acid, HC2H3O2 Nitric acid, HNO3

15. Sulfuric Acid Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining Thick clouds of sulfuric acid are a feature of the atmosphere of Venus. (image provided by NASA)

16. Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive componentsevaporate easily Stains proteins (including skin!)

17. Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive componentsevaporate easily Stains proteins (including skin!)

18. Hydrochloric Acid Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”

19. Phosphoric Acid A flavoring agent in sodas Used in the manufacture of detergents Used in the manufacture of fertilizers Not a common laboratory reagent

20. Acetic Acid Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

21. Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids H3PO4 HCl H2SO4 HC2H3O2 H2CO3 HNO3

22. Acids Effect Indicators Bluelitmus paper turnsredin contact with an acid.

23. Acids Have a pH less than 7

24. Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g) Zn + 2HCl  ZnCl2 + H2(g) Mg + H2SO4 MgSO4 + H2(g)

25. Effects of Acid Rain on Marble(calcium carbonate) George Washington: BEFORE George Washington: AFTER

26. Arrhenuis Base • A base is any Hydroxide that dissolves in water to yield hydroxide ions as the only negative ion • NaOH • KOH • Mg(OH)2

27. Properties of Bases • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns hot pink • Bases have a pH greater than 7 • Bases are proton (hydrogen ion, H+) acceptors • Solutions of bases feel slippery • Bases neutralize acids

28. Examples of Bases Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

29. Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

30. Bases have a pH greater than 7

31. Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

32. Acids Neutralize Bases Neutralization reactions ALWAYS produce a salt and water. HCl + NaOH  NaCl + H2O H2SO4 + 2NaOH  Na2SO4 + 2H2O 2HNO3 + Mg(OH)2 Mg(NO3)2 + 2H2O

33. Acid-Base Titration and pH

34. Self-Ionization of Water H2O + H2O  H3O+ + OH- Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

35. Ion Concentration in Solutions

36. pH Scale

37. Interpreting pH • The term “pH” means power of hydrogen • Refers to the H+ ions released by the acids to form H3O+ ions • The more H+ released the more H3O+ and the lower the pH and stronger the acid • The lower the pH the greater the power of Hydrogen

38. pH • The negative logarithm , to the base 10, of the H+ concentration • The log to the base 10 of a power 10 is equal to the power • -log [10-7] = 7

39. H+, OH-, and pH

40. Calculating pH, pOH pH = -log10(H3O+) pOH = -log10(OH-) Relationship between pH and pOH pH + pOH = 14 Finding [H3O+], [OH-] from pH, pOH [H3O+] = 10-pH [OH-] = 10-pOH

41. Kw – Ionization Constant for Water In pure water at 25 C: [H3O+] = 1 x 10-7 mol/L [OH-] = 1 x 10-7 mol/L Kw is a constant at 25 C: Kw = [H3O+][OH-] Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14

42. Titrations • The molarity of an acid (or base) of unknown concentration can be determined by slowly combining it with a base(or acid) of known molarity(standard solution) until neutralization occurs • A method of determining the concentration of an acid or base by neutralizing it with a solution of known concentration • The end point is determined by the use of indicators. (endpoint – when the right amount of standard solution has been added and neutralization as occurred)

44. Titration • Moles = Volume x Molarity • naVaMa = nbVbMb • na = # of H+ ions Ma = Molarity of acid • nb = # of OH- ions Mb = Molarity of base • Va = Volume of acid • Vb = Volume of base

45. pH Calculations

46. Measuring pH with wide-range paper

47. Narrow-Range pH Paper

48. Indicators • An indicator is a weak acid (or base) that changes its color in a known pH range when it gains or loses a H+ ion. • Phenolphthalein is a common indicator that is colorless when it is protonated (contains a H+) when it reacts with a base it loses it H+ and turns pink

49. Measuring pH • Phenolphthalein changes from colorless to pink at pH 7–9.

50. 19.2 Measuring pH