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2 Acids and Bases

3 Common Acids & Bases

4 Examples AcidsBases Lemon Juice Ammonia Vinegar Baking Soda Muriatic Acid Chocolate

5 Examples AcidsBases Sulfuric Lye Lactic Washing Soda Boric Milk of Magnesia

6 Examples AcidsBases Coke Limestone Vitamin C Fireplace ashes Aspirin Detergents

7 Acid Properties sour taste change the color of litmus from blue to red. react with –metals such as zinc and magnesium to produce hydrogen gas –hydroxide bases to produce water and an ionic compound (salt) –carbonates to produce carbon dioxide.

8 Base Properties bitter or caustic taste a slippery, soapy feeling the ability to change litmus red to blue changes phenolphthalein to red the ability to interact with acids react with ammonium salts to produce ammonia gas

9 Ashes and water make a slippery alkaline solution once used to clean hands.

10 The Six Strong Acids HCl (aq) HBr (aq) HI (aq) H 2 SO 4(aq) HNO 3(aq) HClO 4(aq) Hydrochloric acid Hydrobromic acid Hydroiodic acid Sulfuric acid Nitric acid Perchloric acid

11 The Strong Bases Group 1A Metal Hydroxides: Ba(OH) 2(aq) Sr(OH) 2(aq) LiOH (aq) NaOH (aq) KOH (aq) CsOH (aq)

12 Svante Arrhenius was a Swedish scientist who lived from In 1884 he advanced a theory of acids and bases.

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14 An Arrhenius acid “is a hydrogen- containing substance that dissociates to produce hydrogen ions.” HA → H + + A - acid

15 An Arrhenius base is a hydroxide- containing substance that dissociates to produce hydroxide ions in aqueous solution. MOH → M + (aq) + OH - (aq) base

16 An Arrhenius acid solution contains an excess of H + ions. An Arrhenius base solution contains an excess of OH - ions. If an acid is neutralized by adding base: –the equiv of the acid = the equiv of the base. H + = OH –

17 J.N. Brönsted ( ) was a Danish chemist and T. M. Lowry ( ) was an English chemist. In 1923 they advanced their theory of acids and bases.

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19 A Brönsted acid is a proton (H + ) passer. A Brönsted base is a proton (H + ) receiver.

20 proton passer proton receiver HCl (aq) + H 2 O (l) → H 3 O + (aq) + Cl – (aq) Brönsted Acid Brönsted Base

21 hydrogen ion does not exist in water hydrogen ion combines with water a hydronium ion is formed

22 HCl(g) → Cl - (aq) baseacid Conjugate acid-base pairs differ by a proton (H + ). When an acid passes a proton it becomes the conjugate base.

23 Conjugate acid-base pairs differ by a proton (H + ). When a base accepts a proton it becomes the conjugate acid. H 3 O + (aq)H 2 O (l) → acidbase

24 Conjugate acid-base pairs differ by a proton (H + ). baseacid HCl(g)+ → Cl - (aq)+H 3 O + (aq)H 2 O (l) acidbase

25 In 1923 G. N. Lewis developed a more comprehensive theory of acids and bases. The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

27 A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor.

28 Lewis Acid Electron Pair Acceptor Lewis Base Electron Pair Donor Electron pair donated to H +

29 Lewis Acid Electron Pair Acceptor Lewis Base Electron Pair Donor Electron pair donated to B

30 Acid–Base Definitions TheoryAcidBase Arrhenius A hydrogen- containing substance that produces hydrogen ions in water A hydroxide- containing substance that produces hydroxide ions in water BrönstedA proton (H + ) passerA proton (H + ) receiver Lewis Any species that will accept an electron pair Any species that donates an electron pair

31 Reactions of Acids

32 In aqueous solution, the H + or H 3 O + ions are responsible for the characteristic reactions of acids.

33 Reaction with Metals Acids react with metals that lie above hydrogen in the activity series of elements to produce hydrogen and an ionic compound (salt): 2HCl(aq) + Ca(s) → H 2 (g) + CaCl 2 (aq) acid + metal → hydrogen + ionic compound 2H 2 SO 4 (aq) + Mg(s) → H 2 (g) + MgSO 4 (aq)

34 3Zn(s) + 8HNO 3 (dilute) → 3Zn(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen:

35 HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: 2HNO 3 (aq) + Ca(OH) 2 (aq) → Ca(NO 3 ) 2 (aq) + 2H 2 O(l) acidbasesalt acidbasesalt

36 2HBr(aq) + K 2 O(s) → 2KBr(aq) + H 2 O(l) Reaction with Metal Oxides In an aqueous solution the products are a salt and water. This type of reaction is closely related to that of an acid with a base: 2H 2 SO 4 (aq) + MgO(s) → MgSO 4 (aq) + H 2 O(l) acidmetal oxidesalt acidsaltmetal oxide

37 Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: 2HCl(aq) + Na 2 CO 3 (aq) → 2NaCl(aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt H 2 SO 4 (aq) + MgCO 3 (s) → MgSO 4 (aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt HCl(aq) + NaHCO 3 (aq) → NaCl(aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt

38 H 2 CO 3 (aq) → CO 2 (g) + H 2 O(l) Carbonic acid (H 2 CO 3 ) is not the product when an acid reacts with a carbonate because carbonate spontaneously decomposes into carbon dioxide and water.

39 Reactions of Bases

40 HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) Reaction with Acids The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: 2HNO 3 (aq) + Ca(OH) 2 (aq) → Ca(NO 3 ) 2 (aq) + 2H 2 O(l) acidbasesalt acidbasesalt

41 Amphoteric Hydroxides Hydroxides of certain metals are amphoteric, meaning they are capable of reacting as either an acid or a base: Zn(OH) 2 + 2KOH(aq) → K 2 Zn(OH) 4 (aq) + H 2 O(l) Lewis acidbase Zn(OH) 2 + 2HCl(aq) → ZnCl 2 (aq) + 2H 2 O(l) baseacidsalt

42 Reaction of NaOH and KOH with Certain Metals Some amphoteric metals react directly with the strong bases sodium hydroxide and potassium hydroxide to produce hydrogen: 2NaOH(aq) + Zn(s) + 2H 2 O(l) → Na 2 Zn(OH) 4 (aq) + 3H 2 (g) base + metal + water → salt + hydrogen 2KOH(aq) + 2Al(s) + 6H 2 O(l) → 2KAl(OH) 4 (aq) + 3H 2 (g) Lewis acid

43Salts

44 Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH - and O 2- excluded). Chemists use the terms ionic compound and salt interchangeably. Salts are usually crystalline and have high melting and boiling points.

45 NaOHHCl NaCl base acid salt The positive ion of the salt is derived from the base. The negative ion of the salt is derived from the acid. Salt Formation

46 Electrolytes and Nonelectrolytes

47 Electrolytes are substances whose aqueous solutions conduct electricity. Nonelectrolytes are substances whose aqueous solutions do not conduct electricity. Electrolytes are capable of producing ions in solution. Nonelectrolytes are not capable of producing ions in solution.

48 Classes of compounds that are electrolytes are: –acids –bases –salts –solutions of oxides that form an acid or a base

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50 Dissociation and Ionization of Electrolytes

51 Dissociation is the process by which the ions of a salt separate as the salt dissolves.

52 In a crystal of sodium chloride, positive sodium ions are bonded to negative chloride ions.

53 In aqueous solution the sodium and chloride ions dissociate from each other.

54 In aqueous solution the sodium and chloride ions dissociate from each other.

55 Na + and Cl - ions hydrate with H 2 O molecules.

56 The equation representing the dissociation of NaCl is: NaCl(s) + (x+y)H 2 O → Na + (H 2 O) x + Cl - (H 2 O) y The equation can be written more simply as: NaCl(s) → Na + (aq) + Cl - (aq)

57 Ionization is the formation of ions. Ionization occurs as the result of a chemical reaction of certain substances with water.

58 Acetic acid ionizes in water to form acetate ion and hydronium ion. HC 3 H 3 O 2 + H 2 O H 3 O + + C 2 H 3 O 2 - → → acid baseacid base HC 3 H 3 O 2 H + + C 2 H 3 O 2 - → → The equation can be written more simply as: In the absence of water ionization reactions do not occur.

59 Strong and Weak Electrolytes

60 Strong Electrolyte An electrolyte that is essentially 100% ionized in aqueous solution. Weak Electrolyte An electrolyte that is ionized to a small extent in aqueous solution.

61 Most salts are strong electrolytes. Strong acids and bases (highly ionized) are strong electrolytes. Weak acids and bases (slightly ionized) are weak electrolytes.

62 HCl Solution HC 2 H 3 O 2 Solution Strong AcidWeak Acid1% ionized 100% ionized

63 HC 2 H 3 O 2 (aq) → H + (aq) + C 2 H 3 O 2 (aq) → → Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution. ionizedunionized

64 HNO 3 (aq) → H + (aq) + NO 3 (aq) HNO 3, a strong acid, is 100 % dissociated. HNO 2 (aq) → H + (aq) + NO 2 (aq) → → HNO 2, a weak acid, is only slightly ionized.

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66 Electrolytes yield two or more ions per formula unit upon dissociation. NaOH → Na + (aq) + OH - (aq) Na 2 SO 4 → 2Na + (aq) + SO 4 - (aq) two ions in solution per formula unit Fe 2 (SO 4 ) 3 → 2Fe 3+ (aq) + 3SO 4 - (aq) three ions in solution per formula unit five ions in solution per formula unit

67 Electrolytes yield two or more moles per mole of electrolyte upon dissociation. NaOH → Na + (aq) + OH - (aq) 1 mole Na 2 SO 4 → 2Na + (aq) + SO 4 - (aq) 1 mole2 moles1 mole Fe 2 (SO 4 ) 3 → 2Fe 3+ (aq) + 3SO 4 - (aq) 1 mole2 moles3 moles

68 Colligative Properties of Electrolyte Solutions

69 Substances that form ions in aqueous solutions change the colligative properties of water in proportion to the number of ions formed. NaOH → Na + (aq) + OH - (aq) 1 mole Two moles of ions will depress the freezing point of water twice that of one mole of a nonelectrolyte. Fe 2 (SO 4 ) 3 → 2Fe 3+ (aq) + 3SO 4 - (aq) 1 mole2 moles3 moles Five moles of ions will depress the freezing point of water five times that of one mole of a nonelectrolyte.

70 Formulas for Calculations Δt f = i  m  K f Δt b = i  m  K b i = ion multiplier

71 Calculate kilograms of H 2 O A solution is made by dissolving 6.57 g of ammonium chloride (NH 4 Cl) in 50.0 g H 2 O. What is the boiling point of the solution? Calculate moles of NH 4 Cl:

72 A solution is made by dissolving 6.57 g of ammonium chloride (NH 4 Cl) in 50.0 g H 2 O. What is the boiling point of the solution? Calculate the unionized boiling point elevation. Calculate the ion multiplier. NH 4 Cl → NH 4 + (aq) + Cl – (aq) i = 2

73 A solution is made by dissolving 6.57 g of ammonium chloride (NH 4 Cl) in 50.0 g H 2 O. What is the boiling point of the solution? Calculate the ionized boiling point elevation. boiling point solution = boiling point solvent + Δt b. = 100 o C o C = o C 1.25  C  2 = 2.5  C

74 Go Back To Chapter 14 Slide 105

75 Ionization of Water

76 Water ionizes slightly. acidbaseacidbase H 2 O + H 2 O → H 3 O + + OH – → → hydronium ion hydroxide ion H 2 O → H + + OH – → → Water ionization can be expressed more simply as: [H 3 O + ] or [H + ] = 1.0 x mol/L [OH – ] = 1.0 x mol/L Two out of every 1 billion water molecules are ionized.

77 Since both H + and OH – are produced in equal amounts, [H + ]  [OH – ] = 1.0 x mol/L A special constant is applied to this product called the water constant, K w Variations include: K w = [H + ]  [OH – ]

78 Find the [OH – ] in M H 2 SO 4. Assume that H 2 SO 4 is 100% ionized. Since this is an acid solution, we must first find [H + ]. = 0.01 M Since 1 mole H + = 1 equiv, [H + ] = N acid

79 Introduction to pH

80 Math Magic

81 The [H + ] in orange juice is 2.0  10 –4. Change the [H + ] to a more comprehensible number. [H + ] in orange juice is 2.0  10 –4. Change 2.0 into an exponent of base 10 by finding the logarithm: Log 2.0 by calculator is This means that 2.0 =  10 –4 =  10 –4 = –4 = 10 –3.699 Use the exponent with the sign reversed as our measure of the acidity. Let’s call it pH. So pH = 3.7

82 Typical [H + ] in common substances substance logpH Lemon juice– Vinegar– Orange juice– Coffee– Rain– Milk– Blood–

83 pH is the negative logarithm of the hydrogen ion concentration. pH = -log[H + ]

84 Calculation of pH

85 pH = -log[H + ] [H + ] = 1 x when this number is exactly 1 pH = this number without the minus sign. pH = 5

86 pH = -log[H + ] [H + ] = 2 x when this number is between 1 and 10 The number of decimal places of a logarithm is equal to the number of significant figures in the original number. pH is between this number and the next lower number (between 4 and 5). one significant figure pH = 4.7 one decimal place

87 The pH scale of Acidity and Basicity

88 pH Loop

89 pHpOH [H + ][OH – ] pH + pOH = 14 [H + ]  [OH – ] = 10 –14 pH = – log [H + ] [H + ] =10 – pH pOH = – log [OH – ] [OH – ] = 10 – pOH Note: [H + ] = normality of the acid [OH – ] = normality of the base

90 pH Loop Calculations

91 Fill-in the Blanks pHpOH[ H + ][ OH – ] 4  10 –  10 –  10 – 6 2

92 Fill-in the Blanks Answers pHpOH[ H + ][ OH – ]  10 –  10 –  10 –7 1.2  10 –  10 –11 3  10 –  10 –8 1  10 –  10 –9 4.0  10 –  10 –  10 –  10 –12 1  10 –2

93 Acid Rain

94 Acid rain: any atmospheric precipitation that is more acidic than usual.

95 pH of rain is lower in the eastern US and higher in the western US. Unpolluted rain has a pH of 5.6 because of carbonic acid formation in the atmosphere. CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) H + + HCO 3 – → ← → ←

96 2.transportation of these oxides into the atmosphere 3.chemical reactions between the oxides and water forming sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) 4.rain or snow, which carries the acids to the ground Process of Acid Rain Formation 1.emission of nitrogen and sulfur oxides into the air From the burning of fossil fuels.

97 2.aluminum is leached from the soil into lakes and adversely affects fish gills. 3.the waxy protective coat on plants is dissolved making them vulnerable to bacteria and fungal attack Effects of Acid Rain 1.freshwater plants and animals decline significantly when rain is acidic

98 Effects of Acid Rain 4.it is responsible for extensive and continuing damage to buildings, monuments and statues

99 Effects of Acid Rain

100 Effects of Acid Rain Smoky Mountains

101 Cleopatra's Needle in New York City Central Park (originally erected in the Egyptian city of Heliopolis on the orders of Thutmose III, around 1450 B.C.). Erected in New York in 1881.

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