4.弱碱(A+弱酸(HB)溶液的pH(K1(HA)>K1(HB) 质子条件:[H+HA=B]+|OH 精确表达式: K (HB).HB]+K 1+A/K (HA) 近似式:+1/Kn(HB)[HB A/K CHA) 最简式:m1=/(HB)kuB 若c(HB=c(A) (A) 与两性物相同)H]=√K(HB)K(HA)
16 4. 弱碱(A- )+弱酸(HB) 溶液的pH(Ka (HA) >Ka (HB)) 质子条件: [H+ ] + [HA] = [B- ] + [OH- ] 精确表达式: 近似式: 最简式: 若c(HB)=c(A- ), (与两性物相同) a w a - (HB) [HB] [H ] 1 [A ]/ (HA) K K K + + = + a a - (HB) (HA) (HB) [H ] (A ) KKc c + = a a [H ] (HB) (HA) K K + = a a - (HB) [HB] [H ] [A ]/ (HA) K K + =
例5计算010moL1Ac+020molL1 H3BO3溶液的pH 解: K2(HAc)=104.6,K2(H3BO3)=10924 HtI Ka(H3 BO3).Ka(HAC).c(H3B03) C(AC) pH=685
17 例5 计算0.10mol·L-1 Ac- + 0.20mol·L-1 H3BO3 溶液的pH . 解： Ka (HAc)=10-4.76 , Ka (H3BO3 )=10-9.24 3 3 3 - a a 3 (H BO ) (HAc) ( H [H ] BO ) (Ac ) K c c + K = pH=6.85