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Chapter 18 Acid-bas - Chapter 18.1 18.2 18 Acid-Base...

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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 produce H + ions and all Arrhenius bases produce OH - ions in aqueous solution. Neutralization involves the combination of H + ions and OH - ions to produce water molecules. It was this single reaction for all strong acid-base neutralizations which according to Arrhenius produced the identical heat of neutralization reaction value of - 56 kJ per mole of water formed. 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 Arrhenius acid/base concept. Also, it limited a base to a substance that contains OH in their formula. NH 3 does not contain OH in its formula but produces OH - ions in H 2 O. 18.4 Weak acids exist mainly as undissociated molecules in water. The words "strong" and "weak" refer to the extent of dissociation in water. Strong acids are essentially 100% dissociated in water. 18.5 (a), (c) and (d) 18.6 (a) 18.7 (b) and (d) 18.8 (b) 18.9 a) HCN( aq ) + H 2 O( l ) h H 3 O + ( aq ) + CN - ( aq ) K a = 3 [H O ] [CN ] [HCN] + - b) HCO 3 - ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + CO 3 2 - ( aq ) K a = 2 3 3 3 [H O ] [CO ] [HCO ] - + - c) HCOOH( aq ) + H 2 O( l ) h H 3 O + ( aq ) + HCOO - ( aq ) K a = 3 [H O ] [HCOO ] [HCOOH] + - 18.10 a) CH 3 NH 3 + ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + CH 3 NH 2 ( aq ) K a = 3 3 2 3 3 [H O ] [CH NH ] [CH NH ] + + b) HClO( aq ) + H 2 O( l ) h H 3 O + ( aq ) + ClO - ( aq ) K a = 3 [H O ] [ClO ] [HClO] + - c) H 2 S( aq ) + H 2 O( l ) h H 3 O + ( aq ) + HS - ( aq ) K a = 3 2 [H O ] [HS ] [H S] + - 75
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18.11 a) HNO 2 ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + NO 2 - ( aq ) K a = 3 2 2 [H O ] [NO ] [HNO ] - + b) CH 3 COOH( aq ) + H 2 O( l ) h H 3 O + ( aq ) + CH 3 COO - ( aq ) K a = 3 3 3 [H O ] [CH COO ] [CH COOH] + - c) HBrO 2 ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + BrO 2 - ( aq ) K a = 3 2 2 [H O ] [BrO ] [HBrO ] - + 18.12 a) H 2 PO 4 - ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + HPO 4 2 - ( aq ) K a = 2 3 4 2 4 [H O ] [HPO ] [H PO ] - + - b) H 3 PO 2 ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + H 2 PO 2 - ( aq ) K a = 3 2 2 3 2 [H O ] [H PO ] [H PO ] - + c) HSO 4 - ( aq ) + H 2 O( l ) h H 3 O + ( aq ) + SO 4 2 - ( aq ) K a = 2 3 4 4 [H O ] [SO ] [HSO ] - + - 18.13 CH 3 COOH < HF < HIO 3 < HI 18.14 HCl HNO 2 HClO HCN 18.15 a) weak acid b) strong base c) weak acid d) strong acid 18.16 a) weak base b) strong base c) strong acid d) weak acid 18.17 a) strong base b) strong acid c) weak acid d) weak acid 18.18 a) weak base b) strong acid c) weak acid d) weak acid 18.19 Autoionization reactions occur when a proton (or, less frequently, another ion) is transferred from one molecule of the substance to another molecule of the same substance. H 2 O( l ) + H 2 O( l ) h H 3 O + ( aq ) + OH - ( aq ) H 2 SO 4 ( l ) + H 2 SO 4 ( l ) h H 3 SO 4 + ( solvated ) + HSO 4 - ( solvated ) 18.20 K C = 3 2 2 [H O ] [OH ] [H O] + - K w = [H 2 O] 2 K C = [H 3 O + ] [OH - ] 18.21 a) pH increases by a value of 1 b) [H 3 O + ] increases by a factor of 100 76
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18.22 a) K a = 4 x 10 - 5 . The smaller value of K a indicates the weaker acid (higher pH). b) p K a = 3.5. The larger p K a indicates the weaker acid. c) 0.01 M . The lower the concentration, the lower [H 3 O + ]. d) 0.1 M weak acid. Less dissociation will lead to a higher pH value.
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