1. Acids & Bases

2. Arrhenius acid is a substance that produces H + in water Arrhenius base is a substance that produces OH - in water Arrhenius Definition of Acids and Bases

3. Properties of Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Acids cause color changes in plant dyes, for example, they change the color of litmus from blue to red. Aqueous acid solutions conduct electricity. 2HCl (aq) + Mg (s) MgCl 2 (aq) + H 2 (g) 2HCl (aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O (l)

4. Properties of Bases Have a bitter taste. Feel slippery. Many soaps contain bases. Bases cause color changes in plant dyes, for example, they change the color of litmus from red to blue. Aqueous base solutions conduct electricity.

5. Brønsted Definition of Acids and Bases Base is a proton acceptor Acid is a proton* donor * In solution exists as a hydrated proton (H 3 O + ) or hydronium ion.

6. Hydronium ion, hydrated proton, H 3 O +

7. Strong acids for all practical purposes are completely ionized in water. Weak acids ionize only to a limited extent in water. Strong bases for all practical purposes are completely ionized in water. Weak bases ionize only to a limited extent in water.

8. Monoprotic acids HCl H + + Cl - HNO 3 H + + NO 3 - CH 3 COOH H + + CH 3 COO - Strong electrolyte, strong acid Weak electrolyte, weak acid Diprotic acids H 2 SO 4 H + + HSO 4 - HSO 4 - H + + SO 4 2- Strong electrolyte, strong acid Weak electrolyte, weak acid Triprotic acids H 3 PO 4 H + + H 2 PO 4 - H 2 PO 4 - H + + HPO 4 2- HPO 4 2- H + + PO 4 3- Weak electrolyte, weak acid

9. Amphoteric: refers to a substances that can act as both a Brønsted acid and a Brønsted base acid base acid

10. spectator ions Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O H + + Cl - + Na + + OH - Na + + Cl - + H 2 O H + + OH - H 2 O net equation molecular equation An ionic compound made up of a cation other than H + and an anion other than OH - or O 2-.

11. acid 2 base 1 acid 1 base 2 acid conjugate base base conjugate acid Conjugate Acid-Base Pairs Defined as an acid and its conjugate base or a base and its conjugate acid. The word conjugate means “joined”.

13. Conjugate acid-base pairs: The conjugate base of a strong acid has no measurable strength. H 3 O + is the strongest acid that can exist in aqueous solution. The OH - ion is the strongest base that can exist in aqeous solution.

14. A Lewis acid is a substance that can accept a pair of electrons A Lewis base is a substance that can donate a pair of electrons Lewis Definition of Acids and Bases H+H+ H O H + OH - acidbase N H H H H+H+ + acidbase N H H H H +

17. O H H+ O H H O H HH O H - + [] + Acid-Base Properties of Water H 2 O + H 2 O H 3 O + + OH - acid conjugate base base conjugate acid autoionization of water

18. The Ion Product of Water The ion-product constant (K w ) is the product of the molar concentrations of H + and OH - ions at a particular temperature. At 25 0 C K w = [H + ][OH - ] = 1.0 x 10 - 14 [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution Is neutral acidic basic

20. pH – A Measure of Acidity [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution Is neutral acidic basic [H + ] = 1 x 10 -7 [H + ] > 1 x 10 -7 [H + ] < 1 x 10 -7 pH = 7 pH < 7 pH > 7 At 25 0 C pH[H + ]

21. [H + ][OH - ] = K w = 1.0 x 10 -14 -log [H + ] – log [OH - ] = 14.00

25. Temperature Dependence of K w and pH Le Châtelier’s principle: the equilibrium of an endothermic process will shift in the direction of products when the temperature is increased, leading to a corresponding increase in the equilibrium constant.

27. Strong Acid: HCl Weak Acid: HF

28. HA (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) Weak Acids (HA) and Acid Ionization Constants HA (aq) H + (aq) + A - (aq) K a is the acid ionization constant KaKa weak acid strength

30. Solvent leveling: All acids with K a >1 will yield identical H 3 O + concentrations in water, independent of their individual K a values The strongest acid that can exist in aqueous solution is the hydronium ion (H 3 O + ). K a = 1 Proton exchange reaction:

31. Weak Bases and Base Ionization Constants K b is the base ionization constant KbKb weak base strength

32. Solvent leveling: All bases with K b >1 will yield identical OH - concentrations in water, independent of their individual K b values The strongest base that can exist in aqueous solution is the hydroxide ion (OH - ). K b = 1 Proton exchange reaction:

34. Ionization Constants of Conjugate Acid-Base Pairs HA (aq) H + (aq) + A - (aq) A - (aq) + H 2 O (l) OH - (aq) + HA (aq) KaKa KbKb H 2 O (l) H + (aq) + OH - (aq) KwKw K a K b = K w Weak Acid Conjugate Base Ka =Ka = KwKw KbKb Kb =Kb = KwKw KaKa

39. Ionization Constants for Diprotic and Triprotic Acids

43. Solving weak acid ionization problems: 1.Identify the major species that can affect the pH. In most cases, you can ignore the autoionization of water. Ignore [OH - ] because it is determined by [H + ]. 2.Use initial concentration and change to express the equilibrium concentrations in terms of single unknown x. 3.Write K a in terms of equilibrium concentrations. Solve for x by the approximation method. 4, If approximation is not valid, solve for x exactly. 5. Calculate concentrations of all species and/or pH of the solution.

47. Percent Ionization For a monoprotic acid HA Percent ionization = [H + ] [HA] 0 x 100% [HA] 0 = initial concentration

52. pH of Dilute Acid and Base Solutions Dilute Solutions of Weak Acids mass balance charge balance Use if H + ion concentration is expected to be less than 10 -6 M. If neglect K w Very Dilute Solutions of Strong Acids

55. pH of Diprotic and Triprotic Acids Concentration of H + ions is the product of only the first stage of ionization. Concentration of the conjugate base for the second stage of ionization is numerically equal to

59. Molecular Structure and Acid Strength H X H + + X - The stronger the bond The weaker the acid HF << HCl < HBr < HI

60. Molecular Structure and Acid Strength Z O HZ O-O- + H + -- ++ The O-H bond will be more polar and easier to break if: Z is very electronegative or Z is in a high oxidation state

61. Molecular Structure and Acid Strength 1. Oxoacids having different central atoms (Z) that are from the same group and that have the same oxidation number. Acid strength increases with increasing electronegativity of Z H O Cl O O H O Br O O Cl is more electronegative than Br HClO 3 > HBrO 3

63. Molecular Structure and Acid Strength 2. Oxoacids having the same central atom (Z) but different numbers of attached groups. Acid strength increases as the oxidation number of Z increases. HClO 4 > HClO 3 > HClO 2 > HClO

65. Carboxylic Acids Lewis structures can be generalized as: Carboxyl group (-COOH). R is part of the acid molecule Electronegative groups in the R group polarize the –O—H bond thereby increasing acidity Strengths of carboxylic acids depend on the nature of the R group.

69. Acid-Base Properties of Salts Neutral Solutions: Salts containing an alkali metal or alkaline earth metal ion (except Be 2+ ) and the conjugate base of a strong acid (e.g. Cl -, Br -, and NO 3 - ). NaCl (s) Na + (aq) + Cl - (aq) H2OH2O Basic Solutions: Salts derived from a strong base and a weak acid. NaCH 3 COO (s) Na + (aq) + CH 3 COO - (aq) H2OH2O CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq)

73. Acid-Base Properties of Salts Acid Solutions: Salts derived from a strong acid and a weak base. NH 4 Cl (s) NH 4 + (aq) + Cl - (aq) H2OH2O NH 4 + (aq) NH 3 (aq) + H + (aq) Salts with small, highly charged metal cations (e.g. Al 3+, Cr 3+, and Be 2+ ) and the conjugate base of a strong acid. Al(H 2 O) 6 (aq) Al(OH)(H 2 O) 5 (aq) + H + (aq) 3+2+

74. Acid Hydrolysis of Al 3+

75. Acid-Base Properties of Salts Solutions in which both the cation and the anion hydrolyze: K b for the anion > K a for the cation, solution will be basic K b for the anion < K a for the cation, solution will be acidic K b for the anion  K a for the cation, solution will be neutral

77. Salts of Amphoteric Ions

78. Oxides of the Representative Elements In Their Highest Oxidation States

79. Antacids and the Stomach pH Balance NaHCO 3 (aq) + HCl (aq) NaCl (aq) + H 2 O (l) + CO 2 (g) Mg(OH) 2 (s) + 2HCl (aq) MgCl 2 (aq) + 2H 2 O (l)

80. Acid-Base Equilibria and Solubility

81. The common ion effect is the shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substance. The presence of a common ion suppresses the ionization of a weak acid or a weak base. Consider mixture of CH 3 COONa (strong electrolyte) and CH 3 COOH (weak acid). CH 3 COONa (s) Na + (aq) + CH 3 COO - (aq) CH 3 COOH (aq) H + (aq) + CH 3 COO - (aq) common ion The Common Ion Effect

82. Consider mixture of salt NaA and weak acid HA. HA (aq) H + (aq) + A - (aq) NaA (s) Na + (aq) + A - (aq) K a = [H + ][A - ] [HA] [H + ] = K a [HA] [A - ] -log [H + ] = -log K a - log [HA] [A - ] -log [H + ] = -log K a + log [A - ] [HA] Henderson-Hasselbalch equation

86. A buffer solution is a solution of: 1.A weak acid or a weak base and 2.The salt of the weak acid or weak base Both must be present! A buffer solution has the ability to resist changes in pH upon the addition of small amounts of either acid or base. Add strong acid H + (aq) + CH 3 COO - (aq) CH 3 COOH (aq) Add strong base OH - (aq) + CH 3 COOH (aq) CH 3 COO - (aq) + H 2 O (l) Consider an equal molar mixture of CH 3 COOH and CH 3 COONa

87. Buffered SolutionUnbuffered Solution Bromophenol blue: blue-purple >pH 4.6 and yellow< pH 3.0. HCl added

92. HCl H + + Cl - HCl + CH 3 COO - CH 3 COOH + Cl -

95. Maintaining the pH of Blood CA: carbonic anhydrase, HHb: hemoglobin molecule HHbO 2 : Oxyhemoglobin

96. Titrations In a titration a solution of accurately known concentration (standard solution) is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. stoichiometric point – the point at which the acid has completely reacted with or been neutralized by the base. Indicator – substance that changes color at (or near) the stoichiometric point. Slowly add base to unknown acid UNTIL The indicator changes color (pink)

97. pH meter – alternate method to detect the stoichiometric point

98. Strong Acid-Strong Base Titrations NaOH (aq) + HCl (aq) H 2 O (l) + NaCl (aq) OH - (aq) + H + (aq) H 2 O (l) pH Profile for the Titration of a Strong Acid with a Strong Base.

99. Consider the addition of a 0.100 M NaOH solution (from a buret) to an Erlenmeyer flask containing 25.0 mL of 0.100 M HCl.

101. Weak Acid-Strong Base Titrations CH 3 COOH (aq) + NaOH (aq) CH 3 COONa (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) CH 3 COO - (aq) + H 2 O (l) CH 3 COO - (aq) + H 2 O (l) OH - (aq) + CH 3 COOH (aq) pH Profile for the Titration of a Weak Acid with a Strong Base. At stoichiometric point (pH > 7)

107. Strong Acid-Weak Base Titrations HCl (aq) + NH 3 (aq) NH 4 Cl (aq) NH 4 + (aq) + H 2 O (l) NH 3 (aq) + H + (aq) At stoichiometric point (pH < 7) H + (aq) + NH 3 (aq) NH 4 + (aq) pH Profile for the Titration of a Strong Acid with a Weak Base.

111. Acid-Base Indicators HIn (aq) H + (aq) + In - (aq)  10 [HIn] [In - ] Color of acid (HIn) predominates  0.1 [HIn] [In - ] Color of conjugate base (In - ) predominates An indicator is a substance (usually a weak organic acid or base) that has distinctly different colors in its nonionized and ionized forms. The end point of a titration occurs when the indicator changes color.

112. The titration curve of a strong acid with a strong base.

113. pH

118. Precipitation Reactions Precipitate – insoluble solid that separates from solution molecular equation ionic equation net ionic equation Pb 2+ + 2NO 3 - + 2K + + 2I - PbI 2 (s) + 2K + + 2NO 3 - K + and NO 3 - are spectator ions Pb(NO 3 ) 2 (aq) + 2KI (aq) PbI 2 (s) + 2KNO 3 (aq) precipitate Pb 2+ + 2I - PbI 2 (s) PbI 2

119. Pb 2+ + 2I - PbI 2 (s)

120. Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature.

123. Solubility Equilibria AgCl (s) Ag + (aq) + Cl - (aq) K sp = [Ag + ][Cl - ] K sp is the solubility product constant MgF 2 (s) Mg 2+ (aq) + 2F - (aq) K sp = [Mg 2+ ][F - ] 2 Ag 2 CO 3 (s) 2Ag + (aq) + CO 3 2 - (aq) K sp = [Ag + ] 2 [CO 3 2 - ] Ca 3 (PO 4 ) 2 (s) 3Ca 2+ (aq) + 2PO 4 3 - (aq) K sp = [Ca 2+ ] 3 [PO 4 3 - ] 2 Solubility product can be approximated as the product of the molar concentrations of the constituent ions, each raised to the power of its stoichiometric coefficient in the equilibrium equation. Experimental concentrations may differ from ideal depending on concentration and reactions involving any of the ions.

125. Possible relationships between Q and K sp Q = K sp Saturated solution Q < K sp Unsaturated solutionNo precipitate Q > K sp Supersaturated solution Precipitate will form Equilibrium Ion product (Q) Q has the same form as the K sp except that the concentrations of ions are not equilibrium concentrations.

126. Molar solubility (mol L -1 ) is the number of moles of solute dissolved in 1 L of a saturated solution. Solubility (g L -1 ) is the number of grams of solute dissolved in 1 L of a saturated solution. Relating solubility and the K sp

132. Predicting Precipitation Reactions

134. Separation of Ions by Fractional Precipitation

136. The Solubility of a Substance Is Affected by a Number of Factors Common Ion Effect: Common ion Consider a solution containing both AgCl and AgNO 3 The solubility of AgCl is less in a solution of AgNO 3 than in water.

139. pH: The solubilities of many substances are affected by hydronium and/or hydroxide ion concentration [OH - ] is a function of pH. Increasing pH will decrease the solubility. Milk of magnesia, which contains Mg(OH) 2, is used to treat acid indigestion.

140. [F - ] is a function of pH. Decreasing pH will increase the solubility. The solubilities of salts containing anions that do not hydrolyze are unaffected by pH. Examples of such anions are Cl -, Br -, and I -.

145. A complex ion is an ion containing a central metal cation bonded to one or more molecules or ions. Co 2+ (aq) + 4Cl - (aq) CoCl 4 (aq) 2- K f = [CoCl 4 ] [Co 2+ ][Cl - ] 4 2- The formation constant or stability constant (K f ) is the equilibrium constant for the complex ion formation. Co(H 2 O) 6 2+ CoCl 4 2- KfKf stability of complex Complex Ion Equilibria Co 2+ is hydrated in solution as Co(H 2 O) 6 2+.

146. Addition of concentrated NH 3 (aq) to CuSO 4 (aq) blue solution light blue precipitate dark blue complex ion Increasing [NH 3 ]

153. NaCl(aq) added to AgNO 3 (aq)NH 3 (aq) added to AgCl(s) AgCl(s)Ag(NH 3 ) 2 + (aq)

154. Amphoteric hydroxides can react with both acids and bases. Lewis base Lewis acid Soluble in acid Soluble in base

155. Qualitative Analysis of Cations Qualitative analysis: the determination of the types of ions present in a solution. Groups 1 - 5

156. The general procedure for separating ions in qualitative analysis. Add precipitating ion Centrifuge Add precipitating ion Centrifuge

157. A qualitative analysis scheme for separating cations into five ion groups. Add 6M HCl Centrifuge Acidify to pH 0.5; add H 2 S Centrifuge Add NH 3 /NH 4 + buffer(pH 8) Centrifuge Add (NH 4 ) 2 HPO 4 Centrifuge

158. Extra: Step 1 Add NH 3 ( aq ) Centrifuge Step 2 Add HCl Step 3 Add NaOH Centrifuge Step 4 Add HCl, Na 2 HPO 4 Step 5 Dissolve in HCl and add KSCN A qualitative analysis scheme for Ag +,Al 3+,Cu 2+, and Fe 3+

160. A view inside Carlsbad Caverns, New Mexico

161. Flame Test for Cations lithium sodium potassiumcopper