Acids, Bases, and Salts Chapter 19

1. Acids, Bases, and SaltsChapter 19 Chemistry 2

2. http://www.gpb.org/chemistry-physics/physics/1303 • 25 minutes

3. Acid-Base Theories 19.1

4. Section 19.1Acid-Base Theories • OBJECTIVES: • Define the properties of acids and bases.

5. Properties of Acids and Bases 19.1 • Acids • Taste sour/tart (ex: vinegar) • in aqueous solutions = electrolytes (conduct electricity) • Strong or weak • Produce hydrogen gas • React with compounds of hydroxide to produce water and salt • Bases • Taste Bitter (most are hazardous to taste!) (ex: soap, milk of magnesium) • Slippery feeling • When containing hydroxide, reacts with acids to form water and salt

6. Acids Affect Indicators, by changing their color Blue litmus paper turns red in contact with an acid (and red paper stays red).

7. Effects of Acid Rain on Marble(marble is calcium carbonate) George Washington: BEFORE acid rain George Washington: AFTER acid rain

8. Sulfuric Acid = H2SO4 • Highest volume production of any chemical in the U.S. (approximately 60 billion pounds/year) • Used in the production of paper • Used in production of fertilizers • Used in petroleum refining; auto batteries

9. Nitric Acid = HNO3 • Used in the production of fertilizers • Used in the production of explosives • Nitric acid is a volatile acid – its reactive components evaporate easily • Stains proteins yellow (including skin!)

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

11. Phosphoric Acid = H3PO4 • A flavoring agent in sodas (adds “tart”) • Used in the manufacture of detergents • Used in the manufacture of fertilizers • Not a common laboratory reagent

12. Acetic Acid = HC2H3O2 (also called Ethanoic Acid, CH3COOH) • Used in the manufacture of plastics • Used in making pharmaceuticals • Acetic acid is the acid that is present in household vinegar

13. Examples of Bases(metallic hydroxides) • Sodium hydroxide, NaOH(lye for drain cleaner; soap) • Potassium hydroxide, KOH (alkaline batteries) • Magnesium hydroxide, Mg(OH)2(Milk of Magnesia) • Calcium hydroxide, Ca(OH)2(lime; masonry)

14. Bases Affect Indicators Red litmus paper turns blue in contact with a base (and blue paper stays blue). Phenolphthalein turns purple in a base.

15. Arrhenius Acids and Bases 19.1 • Svante Arrhenius (1859 – 1927) • Arrhenius Acids – hydrogen-contain compounds that ionize to yield hydrogen ions in aqueous solution • Monoprotic: 1 ionizablehydrogens - HNO3 • Diprotic: 2 ionizablehydrogens – H2SO4 • Not all compounds containing H are acids and not all acids release H ions • H must be attached to a very electronegative atom/compound • Arrhenius Bases – ionize to yield hydroxide ions in aqueous solutions • Ex: sodium hydroxide, also known as Lye = ionic solid • Some bases are very soluble in water, some are not

16. Polyprotic Acids? • Some compounds have more than one ionizable hydrogento release • HNO3 nitric acid - monoprotic • H2SO4 sulfuric acid - diprotic - 2 H+ • H3PO4 phosphoric acid - triprotic - 3 H+ • Having more than one ionizable hydrogen does not mean stronger!

17. Bronsted-Lowry Acids and Bases 19.1 • Acid = H-ion Donor • Base = H-ion Acceptor • Why Ammonia is a base? • Ammonia – base = acceptor • water – acid = donor • Conjugate Acids and Bases • Conjugate acid= particle formed when a base gains a hydrogen • Conjugate base = particle that remains when an acid donated a H • Hydronium Ion (H3O+) • A substance that acts as both and acid and base = amphoteric • Ex: water

19. Lewis Acids and Bases 19.1 • Gilbert Lewis (1875 - 1946) – yes, Lewis dot structures • Acid – accepts pair of electrons in covalent bond • Base – donates pair of electrons in covalent bond

21. Hydrogen Ions and Acidity 19.2

22. Hydrogen Ions from Water 19.2 • Water = polar = in continuous motion • Motion sometimes create enough energy to transfer H ion from one water molecule to another • Self-ionization of water • If OH- and H+ are in equal number = neutral solution

23. Ion Product Constant for Water 19.2 • Le Chatelier’s Principle – if H+ increases, OH- decreases and vice versa (equilibrium shift) 2H2O H3O+ + OH • Acidic solution – H+ greater than OH- • Basic solution – OH- great than H+ • Aka: alkaline solutions • Equilibrium Constant (Keq) – ratio of concentrations to reactants at equlibrium • Kw = [H+] x [OH-] = 1 x 10-14

26. The pH Concept 19.2 • O – 6.9 = Acidic • 7 = Neutral • 7.1 – 14 = Basic • pH = -log[H+] • pH of a neutral system • pH = -log(1 x 10-7) • = -(log1 + log10-7) • = -(0 + (-7)) • = 7 • pOH = -log[OH-] • pH + pOH= 14

34. Measuring pH 19.2 • Why do you need to know pH? • Correct balance of pool • Soil conditions for growing plants • Medical diagnoses • Can use indicators or pH meter • Page 601 Sample Problem • Practice problems 15 - 16

35. How to measure pH with wide-range paper 1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod. 2.Compare the color to the chart on the vial – then read the pH value.

36. http://www.gpb.org/chemistry-physics/chemistry/1102 • 25 minutes

37. Strengths of Acids and Bases 19.3

38. Strong and Weak Acids and Bases 19.3 • Classified depending on degree of ionization • Strong = completely ionize • Weak = slightly ionize • Equilibrium Constant Expression • Keq (picture uses Kc)

39. Equilibrium Constant Expression The esterification reaction equilibrium A typical equation might be: There is only one molecule of everything shown in the equation. That means that all the powers in the equilibrium constant expression are "1". You don't need to write those into the Kc expression.

40. This time the Kc expression will include some visible powers:

41. Acid Dissociation Constant 19.3 • Ka = ratio of concentration of the dissociated (or ionized) form of an acid to concentration of the undissociated • Reflects fraction of an acid in the ionized form • Ka AKA ionization constants • Ka = small = dissociation is small = weak acid HA(aq) H+(aq) + A-(aq)

42. Strong Acid Dissociation(makes 100 % ions)

43. Weak Acid Dissociation(only partially ionizes)

44. Acid Dissociation Constant 19.3 The Acid Dissociation Constant, Ka, is the equilibrium constant for the reaction in which a weak acid is in equilibrium with its conjugate base in aqueous solution. Notice that in the equilibrium expression below the concentration of water is not included. This is because water is vastly in excess and the amount changes negligibly on equilibrium being established. Ka can be thought of as a modified equilibrium constant. For example, CH3COOH(aq) + H2O(l) = CH3COO-(aq) + H3O+(aq) Ka = [CH3COO-(aq)][H3O+(aq)] / [CH3COOH(aq)] Therefore, the larger the value of Ka, the stronger is the acid. The value is sometimes expressed as the logarithm of its reciprocal, called pKa. Therefore, pKa = -log Ka The smaller the value of pKa the stronger the acid. Kais a better measure of the strength of an acid than pH because adding more water to the acid solution will not change the value of the equilibrium constant Ka, but it will change the H+ ion concentration on which pH depends. In the above reaction, ethanoic acid and ethanoate ions form a conjugate acid-base pair.

45. Base Dissociation Constant 19.3 • Strong base – dissociate completely into metal ions and hydroxide ions • Ex: calcium hydroxide and magnesium hydroxide • Weak base – react with water to form a hydroxide ion and conjugate acid of the base • Ex: ammonia • Kb = ratio of the concentration of the conjugate acid times the concentration of the hydroxide ion to the concentration of the base • Indicates the ability of a weak base to compete with strong hydroxide base for hydrogen ions • Kb is small for weak base

46. Base Dissociation Constant, Kb The Base Dissociation Constant, Kb, is the equilibrium constant for the reaction in which a weak base is in equilibrium with its conjugate acid in aqueous solution. For example, NH3(aq) + H2O(l) = NH4+(aq) + OH-(aq) Kb = [NH4+(aq)][OH-(aq)] / [NH3(aq)] Therefore, the larger the value of Kb, the stronger is the base. The value is sometimes expressed as the logarithm of its reciprocal, called pKb. Therefore pKb = -log Kb The smaller the value of pKb the stronger the base. Kb is a better measure of the strength of a base than pH because adding more water to the base solution will not change the value of the equilibrium constant Kb, but it will change the H+ ion concentration. In the above reaction, ammonium ions and ammonia form a conjugate acid-base pair.

47. Concentration and strength 19.3 • Concentrated/dilute = indicate how much acid/base is dissolved • Refer to moles of acid/base in given volume • Strong/Weak =extent of ionization/dissociation of acid/base • Ex: HCl = strong acid • Gastric juice in stomach is dilute HCl • Ex: Vinegar = dilute weak acid of ethanoic acid

48. Practice • Write the Ka expression for HNO2 • Equation: HNO2↔ H1+ + NO21- • Ka = [H1+] x [NO21-] [HNO2] • Write the Kb expression for NH3 (as NH4OH)