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## The Applicable Range of Ionic Strength for Mixed Ions Coordination Titration

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Abstract

The applicable range of ionic strength of mixed ions coordination titration can be deduced by using the side-reaction coefficient of ionic strength, conditional stability constant and criteria for the accurate coordination titration for mixed icons.

Keywords： Mixed ions coordination titration ; The side-reaction coefficient of ionic strength ; Conditional stability constant

QIAO Cheng-Li. The Applicable Range of Ionic Strength for Mixed Ions Coordination Titration. University Chemistry[J], 2016, 31(8): 94-98 doi:10.3866/PKU.DXHX201508002

$\begin{matrix} M+In=MIn \\ + \\ {{H}^{+}} \\ || \\ HIn \\\end{matrix}$

## 1 副反应系数

Y滴定混合离子(M和N)溶液。假设只有N与Y发生副反应，则把Y和M的反应看成主反应，把Y和N的反应看成是Y发生的副反应，滴定反应的变化为：

$\begin{matrix} M+Y=MY \\ + \\ N\xrightarrow{AAAAAAAA}N+Y=NY \\ || \\ NY \\\end{matrix}$

$\begin{matrix} M+Y=MY \\ |{{I}_{1}}|{{I}_{1}}、N{{I}_{1}}| \\ {{a}_{M}}+{{a}_{Y}}={{a}_{MY}} \\ |{{I}_{1}}|{{I}_{2}}{{I}_{2}}| \\ {{a}_{N}}+{{a}_{Y}}={{a}_{NY}} \\\end{matrix}$

γY、γM、γN、γMY和γNY分别为Y、M、N、MY和NY的活度系数。

## 2 条件稳定常数

KNY=KNYo，则 ${{{{K}'}}_{MIn}}=\frac{{{\gamma }_{M}}{{\gamma }_{Y}}{{K}^{\circ }}_{MY}}{{{\gamma }_{MY}}{{c}_{N}}{{^{s}}^{p1}}{{K}^{\circ }}_{NY}}$ 。KoMY和KNYo分别为MY和NY的活度稳定常数。

## 3 被滴定离子的离子强度允许范围

${{I}_{1}}\le {{\left( \frac{\lg \left( {{c}_{M}}{{^{s}}^{p1}}{{K}^{\circ }}_{MY}/\left( {{c}_{N}}{{^{s}}^{p1}}{{K}^{\circ }}_{NY}+{{a}_{Y\left( H \right)}} \right) \right)\lg {{a}_{MY}}-\lg {{a}_{M}}-5}{0.512\left( {{Z}^{2}}_{M}+{{Z}^{2}}_{Y}-{{Z}^{2}}_{MY} \right)} \right)}^{2}}$

${{I}_{1}}\le {{\left( \frac{\lg \left( {{K}^{\circ }}_{MY}{{K}^{\circ }}_{NY} \right)+\lg {{a}_{MY}}-\lg {{a}_{M}}-5}{0.512\left( {{Z}^{2}}_{M}+{{Z}^{2}}_{Y}-{{Z}^{2}}_{MY} \right)} \right)}^{2}}$

c1sp2、c2sp1 、cisp1和Z1、Z2、Zi等分别为第一化学计量点时，各离子的浓度和电荷数。

${{I}_{1}}\le {{\left( \frac{\lg \left( {{c}_{N}}{{^{s}}^{p1}}{{K}^{\circ }}_{NY} \right)+\lg {{a}_{NY}}-\lg {{a}_{N}}-\lg {{a}_{Y}}-6}{0.512\left( {{Z}^{2}}_{N}+{{Z}^{2}}_{Y}-{{Z}^{2}}_{MY} \right)} \right)}^{2}}$

c1sp2 、c2sp2 、cisp2和Z1、Z2、Zi等分别为第二化学计量点时，各离子的浓度和电荷数。

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