General Chemistry by Whitten, Atwood, Morrison Chapter 19 solutions

General Chemistry by Whitten, Atwood, Morrison Chapter 19 solutions

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210 19 Ionic Equilibria II: Buffers and Titration Curves 19-1 (a) At 25 degrees C, K a = [H + ] [OH - ] = 1.0 x 10 –14 or pH + pOH = 14.00; therefore, pH = 14.00 –pOH. (b) The larger the K a the stronger the acid but any relationship between K a and pH would require that the concentration also be considered. Therefore, there is no common expression that relates K a and pH but you could derive one. (c) Since pH and pOH are related via the expression for K w , the discussion in part (b) above also pertains to possible relationships between K a and pOH. 19-3 (a) The names and formulas of the seven common strong acids include: HNO 3 nitric acid HCl hydrochloric acid HClO 4 perchloric acid HBr hydrobromic acid HClO 3 chloric acid HI hydroiodic acid H 2 SO 4 sulfuric acid (b) Some names and formulas of weak acids are listed in Table 4-6, and others appear in Appendix F. Some weak acids include; HF hydrofluoric acid H 2 CO 3 carbonic acid HCN hydrocyanic acid H 3 PO 4 phosphoric acid 2 nitrous acid H 2 3 sulfurous acid (c) The common strong bases are listed in Table 4-7, and their formulas appear in Table 18-1. LiOH lithium hydroxide NaOH sodium hydroxide KOH potassium hydroxide Ca(OH) 2 calcium hydroxide RbOH rubidium hydroxide Sr(OH) 2 strontium hydroxide CsOH cesium hydroxide Ba(OH) 2 barium hydroxide (d) Names and formulas for five common weak bases appear in Table 18-6; additional ones are listed in Appendix G. Some weak bases include: NH 3 ammonia (CH 3 )NH 2 methylamine N 2 H 4 hydrazine (CH 3 ) 2 dimethylamine C 5 H 5 N pyridine (CH 3 ) 3 N trimethylamine 19-5 SALT (Parents) (a) 2HF + Ca(OH) 2 CaF 2 + H 2 O basic (weak acid/strong base) (b) H 2 S + Zn(OH) 2 ZnS + 2H 2 O basic (weak acid/weak base, but, base is stronger than acid) (c) 3HCl + As(OH) 3 AsCl 3 + 3H 2 O acidic (strong acid/weak base) (d) H 3 4 + 3KOH K 3 4 + 3H 2 O basic (weak acid/strong base) (e) HNO 3 + NH 3 NH 4 NO 3 acidic (strong acid/weak base)
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211 19-7 (a) buffered (a weak acid and its salt) (b) not buffered (a basic salt and a neutral salt) (c) buffered (a weak base and its salt) (d) not buffered (mixture of strong bases) 19-9 This would be a very poor buffer solution because it contains such a low concentration of the conjugate acid (CH 3 NH 3 + ) of the weak base, CH 3 2 . 19-11 pH = p K a + log [OCl - ] [HOCl] = 7.45 + log (0.0500) (0.0250) pH = 7.45 + log 2.00 = 7.45 + 0.301 = 7.75 19-13 (a) [NH 3 ] = 0.50 M ; [NH 4 + ] = 0.40 M ; K b(NH 3 ) = [NH 4 + ][OH ] 3 ] [OH ] = [base] [cation + ] x K b = 0.50 M 0.40 M x 1.8 x 10 –5 = 2.3 x 10 -5 M pOH = –log 2.3 x 10 –5 = 4.64 pH = 14 – pOH = 9.36 (b) [C 6 H 5 2 ] = 0.15 M ; [C 6 H 5 3 + ] = 0.35 M ; K b(C 6 H 5 2 ) = [C 6 H 5 3 + ][OH ] [C 6 H 5 2 ] - ] = [base] [cation + ] x K b = 0.15 M 0.35 M x 4.2 x 10 –10 = 1.8 x 10 -10 M pOH = –log 1.8 x 10 -10 = 9.74 pH = 14 – pOH = 4.26 19-15 (a) pH = 9.55; pOH = 14 – 9.55 = 4.45; [OH ] = 3.55 x 10 –5 M - ] = [base] [cation + ] x K b [base] [cation + ] = ] K b = 3.55 x 10 1.8 x 10 = 2.0 (b) pH = 9.10; pOH = 14 – 9.10 = 4.90; [OH ] = 1.26 x 10 –5 ] = [base] [cation + ] x K b [base] [cation + ] ] K b = 1.26 x 10 1.8 x 10 = 0.70
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212 19-17 Acid only solution: K a = [H + ][CH 3 COO ] [CH 3 COOH] = ( x ) ( x ) (0.30 - x ) = 1.8 x 10 –5 Assume that x << 0.30 x = 2.32 x 10 –3 , [H + ] = 2.32 x 10 –3 M , pH = 2.63 Acid plus its salt solution: K a = + ][CH 3 ] [CH 3 = ( x ) (0.30 - x ) x ) = 1.8 x 10 –5 Assume that x << 0.30 x = 1.8 x 10 –5 , [H + ] = 1.8 x 10 –5 M , pH = 4.74 In preparing the buffer the solution becomes less acid as the salt is added to the acid. The salt is a
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General Chemistry by Whitten, Atwood, Morrison Chapter 19 solutions

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