Chapter 18

Chapter 18 - CHAPTER 18 ACID-BASE EQUILIBRIA 18.1 18.2 The...

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18-1 CHAPTER 18 ACID-BASE EQUILIBRIA 18.1 The Arrhenius definition classified substances as being acids or bases by their behavior in the solvent water. 18.2 All Arrhenius acids contain hydrogen and produce hydronium ion (H 3 O + ) in aqueous solution. All Arrhenius bases contain an OH group and produce hydroxide ion (OH - ) in aqueous solution. Neutralization occurs when each H 3 O + molecule combines with an OH - molecule to form 2 molecules of H 2 O. Chemists found that the H rxn was independent of the combination of strong acid with strong base. In other words, the reaction of any strong base with any strong acid always produced 56 kJ/mol ( H = -56 kJ/mol). This was consistent with Arrhenius’s hypothesis describing neutralization, because all other counter ions (those present from the dissociation of the strong acid and base) were spectators and did not participate in the overall reaction. 18.3 It is limited by the fact that it only classified substances as an acid or base when dissolved in the single solvent water. The anhydrous neutralization of NH 3 ( g ) and HCl( g ) would not be included in the Arrhenius acid/base concept. In addition, it limited a base to a substance that contains OH in its formula. NH 3 does not contain OH in its formula but produces OH - ions in H 2 O. 18.4 Strong acids and bases dissociate completely into their ions when dissolved in water. Weak acids only partially dissociate. The characteristic property of all weak acids is that a significant number of the acid molecules are not dissociated. For a strong acid, the concentration of hydronium ions produced by dissolving the acid is equal to the initial concentration of the undissociated acid. For a weak acid, the concentration of hydronium ions produced when the acid dissolves is less than the initial concentration of the acid. 18.5 a) Water, H 2 O, is an Arrhenius acid because it produces H 3 O + ion in aqueous solution. Water is also an Arrhenius base because it produces the OH - ion as well. b) Calcium hydroxide, Ca(OH) 2 is a base, not an acid. c) Phosphoric acid, H 3 PO 4 , is a weak Arrhenius acid . It is weak because the number of O atoms exceeds the ionizable H atoms by 1. d) Hydroiodic acid, HI, is a strong Arrhenius acid . 18.6 Only (a) NaHSO 4 18.7 Barium hydroxide, Ba(OH) 2 , and potassium hydroxide, KOH, ( b and d ) are Arrhenius bases because they contain hydroxide ions and form OH - when dissolved in water. H 3 AsO 4 and HOCl a) and c) are Arrhenius acids, not bases. 18.8 (b) H 2 O and (d) H 2 NNH 2 both are very weak 18.9 a) HCN( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + CN - ( aq ) K a = [] 3 CN H O HCN −+   b) HCO 3 - ( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + CO 3 2- ( aq ) K a = 2 33 3 CO H O HCO c) HCOOH( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + HCOO - ( aq ) K a = 3 HCOO H O HCOOH
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18-2 18.10 a) CH 3 NH 3 + ( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + CH 3 NH 2 ( aq ) K a = 32 3 33 CH NH H O CH NH + +   b) HClO( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + ClO - ( aq ) K a = [] 3 ClO H O HClO −+ c) H 2 S( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + HS - ( aq ) K a = 3 2 HS H O HS 18.11 a) HNO 2 ( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + NO 2 - ( aq ) K a = 23 2 NO H O HNO b) CH 3 COOH( aq ) + H 2 O( l ) ' H 3 O + ( aq ) + CH
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This note was uploaded on 01/18/2009 for the course CHEM 1C taught by Professor Roland during the Spring '08 term at UCSC.

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Chapter 18 - CHAPTER 18 ACID-BASE EQUILIBRIA 18.1 18.2 The...

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