Acids, Bases and Salts

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Acids, Bases and Salts Chapter 15 : 

1 Acids, Bases and Salts Chapter 15 Hein and Arena Eugene Passer Chemistry Department Bronx Community College © John Wiley and Sons, Inc Version 2.0 12th Edition

15.1Acids and Bases : 

2 15.1Acids and Bases

Acid Properties : 

3 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. These properties are due to the release of hydrogen ions, H+, into water solution.

Acid Properties : 

Acid Properties pH less than 7 Texture like water Indicators: phenophthalein: turns clear Litmus: goes from pink to red React with many metals to produce hydrogen gas 4

Base Properties : 

5 Base Properties bitter or caustic taste a slippery, soapy feeling. the ability to change litmus red to blue the ability to interact with acids

Base Properties : 

Base Properties pH greater than 7 Feel slippery Break down fat in skin Indicators: phenophthalein turns pink Litmus turns blue 6

Svante Arrhenius : 

Svante Arrhenius Svante Arrhenius was a Swedish scientist who lived from 1859-1927. 7 In 1884 he advanced a theory of acids and bases.

Slide 8: 

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

Slide 9: 

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

Slide 10: 

10 An Arrhenius acid solution contains an excess of H+ ions. An Arrhenius base solution contains an excess of OH- ions.

Slide 11: 

11 J.N. Bronsted (1897-1947) was a Danish chemist and T. M. Lowry (1847-1936) was an English chemist. In 1923 they advanced their theory of acids and bases.

Slide 12: 

12 A Bronsted-Lowry acid is a proton (H+) donor. A Bronsted-Lowry base is a proton (H+) acceptor.

Slide 13: 

13 HCl + H2O(l) → H3O+(aq) + Cl-(aq) proton acceptor Bronsted-Lowry Base proton donor Bronsted-Lowry Acid

Slide 14: 

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

Slide 15: 

15 HCl(g) → Cl-(aq) base acid Conjugate acid-base pairs differ by a proton. When an acid donates a proton it becomes the conjugate base.

Slide 16: 

16 Conjugate acid-base pairs differ by a proton. When a base accepts a proton it becomes the conjugate acid. H3O+(aq) H2O (l) → acid base

Slide 17: 

17 Conjugate acid-base pairs differ by a proton.

Slide 18: 

18 Conjugate acid-base pairs differ by a proton.

Slide 19: 

19 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.

Slide 20: 

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

Slide 21: 

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

Slide 22: 

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

Slide 23: 

23

15.2Reactions of Acids : 

24 15.2Reactions of Acids

In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids. : 

25 In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids.

Slide 26: 

26 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) → H2(g) + CaCl2(aq) acid + metal → hydrogen + ionic compound H2SO4(aq) + Mg(s) → H2(g) + MgSO4(aq)

Slide 27: 

27 3Zn(s) + 8HNO3(dilute) → 3Zn(NO3)2 (aq) + 2NO(g) + 4H2O(l) Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen:

Slide 28: 

28 HBr(aq) + KOH(aq) → KBr(aq) + H2O(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: 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

Slide 29: 

29 2HCl(aq) + Na2O(s) → 2NaCl(aq) + H2O(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: H2SO4(aq) + MgO(s) → MgSO4(aq) + H2O(l)

Slide 30: 

30 Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: 2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g) H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g) HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2O(l) + CO2(g)

Slide 31: 

31 H2CO3(aq) → CO2(g) + H2O(l) Carbonic acid (H2CO3) is not the product when an acid reacts with a carbonate because carbonate spontaneously decomposes into carbon dioxide and water.

15.3Reactions of Bases : 

32 15.3Reactions of Bases

Slide 33: 

33 HBr(aq) + KOH(aq) → KBr(aq) + H2O(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: 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

Slide 34: 

34 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) → K2Zn(OH)4(aq) Zn(OH)2 + 2HCl(aq) → ZnCl2(aq) + 2H2O(l)

Slide 35: 

35 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) + 2H2O(l) → Na2Zn(OH)4(aq) + H2(g) base + metal + water → salt + hydrogen 2KOH(aq) + 2Al(s) + 6H2O(l) → 2KAl(OH)4(aq) + 3H2(g) Lewis acid Lewis acid

15.4Salts : 

36 15.4Salts

Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded). : 

37 Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded). Chemists use the terms ionic compound and salt interchangeably. Salts are usually crystalline and have high melting and boiling points.

Slide 38: 

38 NaOH HCl 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

15.5Electrolytes and Nonelectrolytes : 

39 15.5Electrolytes and Nonelectrolytes

Electrolytes are substances whose aqueous solutions conduct electricity. : 

40 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.

Slide 41: 

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

Slide 42: 

42

15.6Dissociation andIonization of Electrolytes : 

43 15.6Dissociation andIonization of Electrolytes

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

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

Slide 45: 

45 In a crystal of sodium chloride positive sodium ions are bonded to negative chloride ions. 15.2

Slide 46: 

46 In aqueous solution the sodium and chloride ions dissociate from each other. 15.2

Slide 47: 

47 In aqueous solution the sodium and chloride ions dissociate from each other. 15.2

Slide 48: 

48 Na+ and Cl- ions hydrate with H2O molecules. 15.2

Slide 49: 

49 The equation representing the dissociation of NaCl is: NaCl(s) + (x+y)H2O → Na+(H2O)x + Cl-(H2O)y The equation can be written more simply as: NaCl(s) → Na+(aq) + Cl-(aq)

Ionization is the formation of ions. : 

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

Acetic acid ionizes in water to form acetate ion and hydronium ion. : 

51 Acetic acid ionizes in water to form acetate ion and hydronium ion. The equation can be written more simply as: In the absence of water, ionization reactions do not occur.

15.7Strong and Weak Electrolytes : 

52 15.7Strong and Weak Electrolytes

Strong Electrolyte An electrolyte that is essentially 100% ionized in aqueous solution. : 

53 Strong Electrolyte An electrolyte that is essentially 100% ionized in aqueous solution.

Slide 54: 

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

Polyatomic acids : 

Polyatomic acids Strong acids IF # of oxygen atoms out number the hydrogens by 2 H2SO4 HNO3 55

Polyatomic acids : 

Polyatomic acids Weak acids: H3PO4, H2CO3, HC2H3O2 56

Bases: release OH- : 

Bases: release OH- Took an electron from a metal Strong: use metals from column 1 or 2 NaOH, Mg(OH)2, KOH, Ca(OH)2 Weak: metal is a transition metal Cu(OH)2, Fe(OH)3, Ag(OH) 57

Slide 58: 

58 15.3

Slide 59: 

59 Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution.

Slide 60: 

60 HNO3, a strong acid, is 100 % dissociated. HNO2, a weak acid, is only slightly ionized.

Slide 61: 

61

Slide 62: 

62 Electrolytes yield two or more ions per formula unit upon dissociation. NaOH → Na+(aq) + OH-(aq) two ions in solution per formula unit three ions in solution per formula unit five ions in solution per formula unit

Slide 63: 

63 Electrolytes yield two or more moles of ions per mole of electrolyte upon dissociation. NaOH → Na+(aq) + OH-(aq)

Colligative Properties ofElectrolyte Solutions : 

64 Colligative Properties ofElectrolyte Solutions

Slide 65: 

65 Substances that form ions in aqueous solutions change the colligative properties of water in proportion to the number of ions formed. Two moles of ions will depress the freezing point of water twice that of one mole of a nonelectrolyte. Five moles of ions will depress the freezing point of water five times that of one mole of a nonelectrolyte.

15.8Ionization of Water : 

66 15.8Ionization of Water

Slide 67: 

67 Water ionizes slightly. hydronium ion hydroxide ion Water ionization can be expressed more simply as: [H3O+] or [H+] = 1.0 x 10-7 mol/L [OH-] = 1.0 x 10-7 mol/L Two out of every 1 billion water molecules are ionized.

15.9Introduction to pH : 

68 15.9Introduction to pH

pH is the negative logarithm of the hydrogen ion concentration. : 

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

Calculation of pH : 

70 Calculation of pH

Slide 71: 

71 pH = -log[H+] [H+] = 1 x 10-5 when this number is exactly 1 pH = 5

The number of decimal places of a logarithm is equal to the number of significant figures in the original number. : 

72 pH = -log[H+] [H+] = 2 x 10-5 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

Slide 73: 

73 What is the pH of a solution with an [H+] of 1.0 x 10-11? pH = - log(1.0 x 10-11) pH = 11.00 2 decimal places 2 significant figures

Slide 74: 

74 What is the pH of a solution with an [H+] of 6.0 x 10-4? pH = - log[H+] = -(3.22) = 3.22 2 decimal places 2 significant figures log[H+] = log (6.0 x 10-4) = -3.22

Slide 75: 

75 What is the pH of a solution with an [H+] of 5.47 x 10-8? pH = - log[H+] = -(7.262) = 7.262 3 decimal places 3 significant figures log[H+] = log(5.47 x 10-8) = -7.262

Slide 76: 

76 The pH scale of Acidity and Basicity 15.4

15.10Neutralization : 

77 15.10Neutralization

Neutralization The reaction of an acid and a base to form a salt and water. : 

78 Neutralization The reaction of an acid and a base to form a salt and water.

Titrations : 

79 Titrations

Slide 80: 

80 Titration The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent.

Slide 81: 

81 42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is The unit of volume when using molarity is liters. Calculate the moles of NaOH that react. Calculate the liters of NaOH that react.

Slide 82: 

82 42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution. The equation for the reaction is The mole ratio of HCl to NaOH is 1:1 The moles of NaOH that react equals the moles of HCl that react. 0.00630 mol NaOH react. 0.00630 mol HCl react. The molarity of the HCl solution is

15.12Acid Rain : 

83 15.12Acid Rain

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

84 Acid rain is any atmospheric precipitation that is more acidic than usual. The increase in acidity might be from natural or industrial sources.

Slide 85: 

85 The 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.

Process of Acid Rain Formation : 

86 transportation of these oxides into the atmosphere chemical reactions between the oxides and water forming sulfuric acid (H2SO4) and nitric acid (HNO3) rain or snow, which carries the acids to the ground Process of Acid Rain Formation emission of nitrogen and sulfur oxides into the air From the burning of fossil fuels.

Effects of Acid Rain : 

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

Effects of Acid Rain : 

88 it reduces the durability of paint and promotes the deterioration of paper, leather and cloth Effects of Acid Rain it is responsible for extensive and continuing damage to buildings, monuments and statues

15.13Colloids : 

89 15.13Colloids

Slide 90: 

90 Colloid A dispersion in which the dispersed particles are larger than the solute ions or molecules of a true solution and smaller than the particles of a mechanical suspension.

Slide 91: 

91 suspension a dispersion in which microscopically visible particles are mixed with, but not dissolved in a fluid or solid.

Slide 92: 

92 Colloid is derived from the Greek word “kolla” meaning “glue.” The term colloid does not imply a system has a gluelike quality.

Slide 93: 

93 The fundamental difference between a colloidal dispersion and a true solution is the size of the particles. In ordinary solutions the size of solute particles range from 0.1 to 1 nm. The size of colloidal particles range from 1 to 1,000 nm. In a solution the particles are usually single ions or molecules. In a colloid the particles are usually aggregations of ions or molecules.

Slide 94: 

94

15.14Properties of Colloids : 

95 15.14Properties of Colloids

Slide 96: 

96 In 1827 Robert Brown illuminated an aqueous suspension of pollen under a high powered microscope. He observed a trembling erratic motion of the pollen grains. This erratic motion is characteristic of colloids in general. This random motion is called Brownian movement.

Slide 97: 

97 When an intense beam of light is passed through an ordinary solution and viewed at an angle, the beam passing through the solution is hardly visible. A beam of light is clearly visible and sharply outlined when it is passed through a colloidal dispersion. This phenomenon is known as the Tyndall effect.

Slide 98: 

98 Colloidal particles have huge surface areas in comparison to the volume of the same particles if they were aggregated into one large particle. Colloidal particles become electrically charged when they adsorb ions on their surfaces. This occurs because surface atoms or ions of the colloid attract and adsorb ions or polar molecules from the dispersion medium.

Slide 99: 

99 The End

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