文档介绍：第四章酸碱平衡与酸碱滴定法 4-1 .将 mol ?L ?1 HAc 溶液稀释到什么体积才能使解离度增加一倍。解: 设稀释到体积为 V ,稀释后 V c mL 300 L mol 20 .0 1????由????1 2acK 得:)21( )2( 300 20 .01 20 .0 22??????????V 因为 K ?a = ? 10 ?5c a= mol ?L ?1c aK ?a> 20K ?wc a/K ?a >500 故由 1 ?2 ?=1 ??得V =[300 ? 4/1]mL =1200mL 此时仍有 c aK ?a >20 K ?wc a/K ?a >500 。 4-2 . 奶油***后的分解产物之一为丁酸(C 3H 7 COOH) , 有恶臭。今有 含 mol ?L ?1 丁酸的溶液, pH 为 , 求丁酸的 K ?a。解: pH= c (H +) =10 ? mol ?L ?1?=10 ? / = ? 10 ?2 K ?a= 52 22210 )10 (20 .01 ?????????????c 4 -3. What is the pH ofa ?L ?1 solution of ammonium acetate at 25℃?pK ?a of acetic acid at 25℃ is , pK ?a of the ammonium ion at 25℃ is , pK w is . 解:c (H + )= 00 .7 24 .9 76 .421 10 10 10 ?????? aaKK pH= ? log c (H +)= 4-4 .已知下列各种弱酸的 K ?a 值,求它们的共轭碱的 K ?b 值,并比较各种碱的相对强弱。(1)HCN K ?a = × 10 ? 10; (2)HCOOH K ?a = × 10 ?4; (3)C 6H 5 COOH( 苯甲酸)K ?a = × 10 ?5; (4) C 6H 5 OH ( 苯酚)K ?a = × 10 ? 10; (5)HAsO 2K ?a = × 10 ? 10; (6) H 2C 2O 4K ? a1 = ? 10 ?2;K ? a2 = ? 10 ?5; 解: (1)HCN K a= ? 10 ? 10K b=K w / ? 10 ? 10 = ? 10 ?5 (2)HCOOH K a= ? 10 ?4K b=K w / ? 10 ?4 = ? 10 ? 11 (3)C 6H 5 COOH K a= ? 10 ?5K b=K w / ? 10 ?5 = × 10 ? 10 (4)C 6H 5 OH K a = ? 10 ? 10K b=K w / ? 10 ? 10 = ? 10 ?5 (5)HAsO 2K a = ? 10 ? 10K b=K w / ? 10 ? 10 = ? 10 ?5 (6)H 2C 2O 4K a1 = ? 10 ?2K