Acids Bases and Salts Chapter 15 Hein and

Acids, Bases and Salts Chapter 15 Hein and Arena Version 2. 0 12 th Edition Eugene Passer Chemistry Department Bronx Community 1 College © John Wiley and Sons, Inc

Chapter Outline 15. 1 Acids and Bases 15. 8 Ionization of Water 15. 2 Reactions of Acids 15. 9 Introduction to p. H 15. 3 Reactions of Bases 15. 10 Neutralization 15. 4 Salts 15. 5 Electrolytes and Nonelectrolytes 15. 6 Dissociation and Ionization of Electrolytes 15. 7 Strong and Weak Electrolytes 15. 11 Writing Net Ionic Equations 15. 12 Acid Rain 15. 13 Colloids 15. 14 Properties of Colloids 2

15. 1 Acids and Bases 3

Acid Properties • sour taste • change the color of litmus from blue to red These properties are due to the release of hydrogen ions, H+, into water solution. • 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. 4

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

• Svante Arrhenius was a Swedish scientist who lived from 1859 -1927. • In 1884 he advanced a theory of acids and bases. 6

An Arrhenius acid “is a hydrogencontaining substance that dissociates to produce hydrogen ions. ” HA → H+ + Aacid 7

An Arrhenius base is a hydroxidecontaining substance that dissociates to produce hydroxide ions in aqueous solution. MOH → M+(aq) + OH-(aq) base 8

An Arrhenius acid solution contains an excess of H+ ions. An Arrhenius base solution contains an excess of OH- ions. 9

• 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. 10

A Bronsted-Lowry acid is a proton (H+) donor. A Bronsted-Lowry base is a proton (H+) acceptor. 11

proton acceptor Bronsted-Lowry Acid Bronsted-Lowry Base proton donor HCl + H 2 O(l) → H 3 O+(aq) + Cl-(aq) 12

ionion ishydrogen ion ahydrogen hydronium does formed not existcombines with water in water 13

Conjugate acid-base pairs differ by a proton. When an acid donates a proton it becomes the conjugate base. HCl(g) → Cl-(aq) acid base 14

Conjugate acid-base pairs differ by a proton. When a base accepts a proton it becomes the conjugate acid. H 2 O (l) → H 3 O+(aq) base acid 15

Conjugate acid-base pairs differ by a proton. HCl(g) + H 2 O (l) → Cl-(aq) + H 3 O+(aq) acid base acid 16

Conjugate acid-base pairs differ by a proton. HCl(g) + H 2 O (l) → Cl-(aq) + H 3 O+(aq) acid base acid 17

• 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. 18

A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor. 19

Electron Pair Lewis Acid Acceptor Electron pair donated to H+ Lewis Base Electron Pair Donor 20

Electron Pair Lewis Acid Acceptor Electron pair donated to B Lewis Base Electron Pair Donor 21

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15. 2 Reactions of Acids 23

In aqueous solution, the H+ or H 3 O+ ions are responsible for the characteristic reactions of acids. 24

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): acid + metal → hydrogen + ionic compound 2 HCl(aq) + Ca(s) → H 2(g) + Ca. Cl 2(aq) H 2 SO 4(aq) + Mg(s) → H 2(g) + Mg. SO 4(aq) 25

Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen: 3 Zn(s) + 8 HNO 3(dilute) → 3 Zn(NO 3)2 (aq) + 2 NO(g) + 4 H 2 O(l) 26

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: HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) acid base salt 2 HNO 3(aq) + Ca(OH)2(aq) → Ca(NO 3)2(aq) + 2 H 2 O(l) acid base salt 27

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: Reaction with Metal Oxides 2 HCl(aq) + Na 2 O(s) → 2 Na. Cl(aq) + H 2 O(l) acid metal oxide salt H 2 SO 4(aq) + Mg. O(s) → Mg. SO 4(aq) + H 2 O(l) acid metal oxide salt 28

Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: 2 HCl(aq) + Na 2 CO 3(aq) → 2 Na. Cl(aq) + H 2 O(l) + CO 2(g) acid carbonate salt H 2 SO 4(aq) + Mg. CO 3(s) → Mg. SO 4(aq) + H 2 O(l) + CO 2(g) acid carbonate salt HCl(aq) + Na. HCO 3(aq) → Na. Cl(aq) + H 2 O(l) + CO 2(g) acid carbonate salt 29

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. H 2 CO 3(aq) → CO 2(g) + H 2 O(l) 30

15. 3 Reactions of Bases 31

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: HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) acid base salt 2 HNO 3(aq) + Ca(OH)2(aq) → Ca(NO 3)2(aq) + 2 H 2 O(l) acid base salt 32

Hydroxides of certain metals are amphoteric, meaning they are capable of reacting as either an acid or a base: Amphoteric Hydroxides Zn(OH)2 + 2 HCl(aq) → Zn. Cl 2(aq) + 2 H 2 O(l) base acid salt Zn(OH)2 + 2 KOH(aq) → K 2 Zn(OH)4(aq) Lewis acid base 33

Reaction of Na. OH and KOH with Certain Metals Some amphoteric metals react directly with the strong bases sodium hydroxide and potassium hydroxide to produce hydrogen: base + metal + water → salt + hydrogen 2 KOH(aq) + 2 Al(s) + 6 H 2 O(l) → 2 KAl(OH)4(aq) + 3 H 2(g) Lewis acid 2 Na. OH(aq) + Zn(s) + 2 H 2 O(l) → Na 2 Zn(OH)4(aq) + H 2(g) Lewis acid 34

15. 4 Salts 35

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). Salts are use Chemists usually the terms crystalline ionic compound and have high and salt interchangeably. melting and boiling points. 36

Salt Formation The negative positive ion of the salt is derived from the acid. base Na. OH HCl acid Na. Cl salt 37

15. 5 Electrolytes and Nonelectrolytes 38

Nonelectrolytes Electrolytes aresubstances whose aqueous solutions do conduct not conduct electricity. Nonelectrolytes Electrolytes areare capable not capable of producing ions in solution. 39

Classes of compounds that are electrolytes are: – acids – bases – salts – solutions of oxides that form an acid or a base 40

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15. 6 Dissociation and Ionization of Electrolytes 42

Dissociation is the process by which the ions of a salt separate as the salt dissolves. 43

In a crystal of sodium chloride positive sodium ions are bonded to negative chloride ions. 44 15. 2

In aqueous solution the sodium and chloride ions dissociate from each other. 45 15. 2

In aqueous solution the sodium and chloride ions dissociate from each other. 46 15. 2

Na+ and Cl- ions hydrate with H 2 O molecules. 47 15. 2

The equation representing the dissociation of Na. Cl is: Na. Cl(s) + (x+y)H 2 O → Na+(H 2 O)x + Cl-(H 2 O)y The equation can be written more simply as: Na. Cl(s) → Na+(aq) + Cl-(aq) 48

the formation of ions. Ionization is occurs as the result of a chemical reaction of certain substances with water. 49

Acetic acid ionizes in water to form acetate ion and hydronium ion. HC 2 H 3 O 2 + H 2 O → H 3 O+ + C 2 H 3 O 2→ Lewis acid Lewis base The equation can be written more simply as: HC 3 H 3 O 2 → H+ + C 2 H 3 O 2→ In the absence of water, ionization reactions do not occur. 50

15. 7 Strong and Weak Electrolytes 51

Strong Electrolyte An An electrolyte that is Weak essentially inaqueoussolution. ionized to a 100% smallionized extent in 52

• Most salts are strong electrolytes • Strong acids and bases (highly ionized) are strong electrolytes. • Weak acids and bases (slightly ionized) are weak electrolytes. 53

HCl 100% Strong Acid Solution ionized HC 2 H 3 O 2 Weak Acid 1% ionized Solution 54 15. 3

Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution. HC 2 H 3 O 2(aq) → H+ (aq) + C 2 H 3 O 2(aq) → unionized 55

HNO 3, a strong acid, is 100 % dissociated. HNO 3(aq) → H+(aq) + NO 3(aq) HNO 2, a weak acid, is only slightly ionized. HNO 2(aq) → H+(aq) + NO 2(aq) → 56

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Electrolytes yield two or more ions per formula unit upon dissociation. Na. OH → Na+(aq) + OH-(aq) two ions in solution per formula unit Na 2 SO 4 → 2 Na+(aq) + SO 4 -(aq) three ions in solution per formula unit Fe 2(SO 4 )3 → 2 Fe 3+(aq) + 3 SO 4 -(aq) five ions in solution per formula unit 58

Electrolytes yield two or more moles of ions per mole of electrolyte upon dissociation. Na. OH → Na+(aq) + OH-(aq) 1 mole Na 2 SO 4 → 2 Na+(aq) + SO 4 -(aq) 1 mole 2 moles 1 mole Fe 2(SO 4 )3 → 2 Fe 3+(aq) + 3 SO 4 -(aq) 1 mole 2 moles 3 moles 59

Colligative Properties of Electrolyte Solutions 60

Substances that form ions in aqueous solutions change the colligative properties of water in proportion to the number of ions formed. Na. OH → 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 → 2 Fe 3+(aq) + 3 SO 4 -(aq) 1 mole 2 moles 3 moles Five moles of ions will depress the freezing point of water five times that of one mole of a nonelectrolyte. 61

15. 8 Ionization of Water 62

Water ionizes slightly. hydroxide ion hydronium ion H 2 O + H 2 O → → H 3 O+ + OHbase → acid base Water ionization can be expressed more simply as: → H+ + OHH 2 O → → [H 3 O+] or [H+] = 1. 0 x 10 -7 mol/L [OH-] = 1. 0 x 10 -7 mol/L 63 Two out of every 1 billion water molecules are ionized.

15. 9 Introduction to p. H 64

p. H is the negative logarithm of the hydrogen ion concentration. p. H = -log[H+] 65

Calculation of p. H 66

p. H = -log[H+] = 1 x 10 -5 when this number is exactly 1 p. H = this number p. Hthe =5 without minus sign. 67

p. H = -log[H+] = 2 x 10 -5 when this number is one significant figure between 1 and 10 p. H is between this number and the next ph = 4. 7 lower number one decimal place (between 4 and 5). The number of decimal places of a logarithm is equal to the number of significant figures in the 68 original number.

What is the p. H of a solution with an [H+] of 1. 0 x 10 -11? 2 significant figures p. H = - log(1. 0 x 10 -11) p. H = 11. 00 2 decimal places 69

What is the p. H of a solution with an [H+] of 6. 0 x 10 -4? 2 significant figures log[H+] = log (6. 0 x 10 -4) = -3. 22 p. H = - log[H+] = -(3. 22) = 3. 22 2 decimal places 70

What is the p. H of a solution with an [H+] of 5. 47 x 10 -8? 3 significant figures log[H+] = log(5. 47 x 10 -8) = -7. 262 p. H = - log[H+] = -(7. 262) = 7. 262 3 decimal places 71

The p. H scale of Acidity and Basicity 72 15. 4

15. 10 Neutralization 73

Neutralization The reaction of an acid and a base to form a salt and water. HCl(aq) + KOH(aq) → KCl(aq) + H 2 O(l) acid base salt 74

Titrations 75

Titration The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent. 76

42. 00 m. L of 0. 150 M Na. OH solution is required to neutralize 50. 00 m. L of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is HCl(aq) + Na. OH(aq) → Na. Cl(aq) + H 2 O(l) acid base salt Calculate the liters of Na. OH that react. The unit of volume when Convert m. L of Na. OH to using molarity is liters of Na. OH Calculate the moles of Na. OH that react. 77

42. 00 m. L of 0. 150 M Na. OH solution is required to neutralize 50. 00 m. L of hydrochloric acid solution. What is the molarity of the acid solution. The equation for the reaction is HCl(aq) + Na. OH(aq) → Na. Cl(aq) + H 2 O(l) acid base salt The molesratio of Na. OH of HClthat to Na. OH react equals is 1: 1 the moles of HCl that react. 0. 00630 mol Na. OH react. 0. 00630 mol HCl react. The molarity of the HCl solution is 78

15. 11 Writing Net Ionic Equations 79

In the formula equation all compounds are written using their molecular or formula expressions. HCl(aq) + KOH(aq) → KCl(aq) + H 2 O(l) acid base salt In the total ionic equation all ions present in solution are written. (H+ + Cl-) + (K+ + OH-) → K+ + Cl- + H 2 O that equation do not participate inthe a chemical In the net. Ions ionic only ions that react + Cl ion does K ion not does react. not reaction are called spectator ions. are written. H+(aq) + OH-(aq) → H 2 O(l) 80

Rules for Writing Equations 1. Strong electrolytes in solution are written in their ionic form. 2. Weak electrolytes are written in their molecular form. 3. Nonelectrolytes are written in their molecular form. 81

4. Insoluble substances, precipitates and gases are written in their molecular forms. 5. The net ionic equation should include only substances that have undergone a chemical change. Spectator ions are omitted from the net ionic equation. 6. Equations must be balanced both in atoms and in electrical charge. 82

Examples 83

2 Ag. NO 3(aq) + Ba. Cl 2(aq) → 2 Ag. Cl(s) + Ba(NO 3)2(aq) formula equation spectator ions (2 Ag+ + ) + (Ba 2+ + 2 Cl-) → 2 Ag. Cl(s) + (Ba 2+ + ) total ionic equation precipitate Ag+ + Cl- → Ag. Cl(s) net ionic equation 84

formula equation spectator ions total ionic equation gas net ionic equation 85

Mg(s) + 2 HCl(aq) → Mg. Cl 2(aq) + H 2(g) formula equation spectator ion Mg(s) + (2 H+ + 2 Cl-) → (Mg 2+ + 2 Cl-)+ H 2(g) total ionic equation Electrical charge on both sides of the equation = +2 Mg + 2 H+ → Mg 2+ + H 2(g) net ionic equation 86

15. 12 Acid Rain 87

Acid rain is any atmospheric precipitation that is more acidic than usual. The increase in acidity might be from natural or industrial sources. 88

• The p. H of rain is lower in the eastern US and higher in the western US. • Unpolluted rain has a p. H 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 → 89 →

Process of Acid Rain Formation 1. emission of nitrogen and sulfur oxides into the air 2. transportation of these oxides into the From the burning of fossil fuels. 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 90

Effects of Acid Rain 1. freshwater plants and animals decline significantly when rain is acidic 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 91

Effects of Acid Rain 4. it is responsible for extensive and continuing damage to buildings, monuments and statues 5. it reduces the durability of paint and promotes the deterioration of paper, leather and cloth 92

15. 13 Colloids 93

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. 94

• Colloid is derived from the Greek word “kolla” meaning “glue. ” • The term colloid does not imply a system has a gluelike quality. 96

• 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. 97

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15. 14 Properties of Colloids 99

• 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. 100

• 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 Thevisible. Tyndall effect occurs because colloidal • A beam lightenough is clearly visiblelight. and particles are of large to scatter sharply outlined when it is passed through a colloidal dispersion. • This phenomenon is known as the Tyndall effect. 101

• 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. 102

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