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M + Y = MY 主反应 OH - ↙↘A ↓H + ↓ 副反应

回顾与复习 被测物 滴定剂 产物 A - + H + = HA K t = K b / K w = 1/ K a = K H HA K a >10 -7 或 K t = K H HA >10 7 可被准确滴定 . （ ∆ pH= ± 0.3 , E= ± 0.2%, c = 0.1mol/L) M n + + Y 4- =MY n-4 K =[MY]/([M][Y] ） K >10 8 可被准确滴定 ? （ ∆ pM= ± 0.2, E= ± 0.1%, c = 0.01mol/L).

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M + Y = MY 主反应 OH - ↙↘A ↓H + ↓ 副反应

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  1. 回顾与复习被测物 滴定剂 产物A- + H+ = HAKt =Kb/Kw =1/Ka =KHHAKa>10-7或Kt =KHHA>107可被准确滴定.（∆pH=±0.3 , E= ± 0.2%, c = 0.1mol/L)M n+ + Y 4- =MY n-4K=[MY]/([M][Y]）K>108可被准确滴定?（∆pM=±0.2, E= ± 0.1%, c = 0.01mol/L)

  2. M + Y = MY主反应 OH-↙↘A ↓H+ ↓ 副反应 MOH MA HY MOHY 或 MHY ︰ ︰ ︰ M(OH)m HnA HkY [M’] = [M]+[MOH]+…+ [M(OH)m]+[MA]+[MA2]+…+[MAn] [Y’] = [Y] +[HY]+[H2Y]…+ [HkY] [(MY)’] = [MY]+[MHY] 在pH低时 [MY]+[MOHY] 在pH高时 因此 K’(MY)=[(MY)’]/ ([M’][Y’])才能反映实际发生的反应

  3. … H+ 例： 用EDTA滴定Zn2+ Zn + Y = ZnY 主反应 OH- H+ Ca2+ OH- 副反应 NH3 H+ CaY ZnHY ZnOHY Zn(OH)+ Zn(NH3)2+ HY ● ● ● ● ●● ● ● ● H6Y αZn(OH) αY(Ca) αY(H) αZnY(H) αZnY(OH)

  4. K’(MY) =[(MY)’]/ ([M’][Y’]) • = [MY]αMY/ ([M]) αM· [Y] αY) • = [MY]/ ([M] [Y] ) · αMY/ (αMαY) • = K(MY) · αMY/ (αMαY) • 或 • log K’(MY) = logK(MY)-log αM -log αY +logαMY 结论: 只要有副反应发生,K’(MY) < K(MY)

  5. 若用同浓度的EDTA滴定M,定量反应,则:K’(MY) =[(MY)’]/ ([M’][Y’])=99.9% CM/(0.1% CM· 0.1%CM) = 1 / 10-6CM即 CM K’(MY) = 106反应完全度达99.9% 若=0.01000mol/L, 则K’(MY) = 108 或 log K’(MY)=8

  6. 处理复杂平衡问题的思路和算法 • Ka n-i+1KHHiAαM K(MY) • →→βi →αY →K’(MY) • K不n-i+1KiαMY • βi = ∏ Ki= K1K2K3 … … Kn • αM(A) = 1+[A] β1+[A]2 β2 … …+[A]nβn • αY(H) = 1+[H] βH1+[H]2 βH2 … …+[H]nβHn • αM =αM(A) +αM(B) … … + (1-p)有P种物质引起副反应 • αY =αY(H) +αY(N) -1

  7. αM(A) = 1+[A] β1+[A]2 β2 … …+[A]nβn • x0 = 1/(αM(A) )= 1/(1+[A] β1+[A]2 β2 … …+[A]nβn) • x1 = [A] β1 /(αM(A) ) • ： ： xi = [A]iβi /(αM(A) ) • αY(H) = 1+[H] βH1+[H]2 βH2 … …+[H]nβHn • x 0 • x1 ： xi

  8. c(Y) ≠ [Y] c(Zn) ≠ [Zn] c(NH3)≈ [NH3] • 一些浓度关系(例4.3, 4.5)

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