饱和甘汞电极（英语：saturated calomel electrode ，缩写为：SCE）是基于元素汞和氯化亚汞之间反应的参比电极。它已被银/氯化银参考电极广泛取代，但甘汞电极以更坚固而著称。饱和甘汞电极中与汞和氯化亚汞（Hg2Cl2 ，又被称为“甘汞”）接触的水相是氯化钾水溶液。电极通常通过作为盐桥的多孔玻璃熔块连接到另一个电极浸入的溶液。这种多孔熔块是盐桥。 饱和甘汞电极的缩写标记法为： Cl − ( 4 M ) | Hg 2 Cl 2 ( s ) | Hg ( l ) | Pt {\displaystyle {\ce {{Cl^{-}}(4M)|{Hg2Cl2(s)}|{Hg(l)}|Pt}}} 电解理论 溶度积 饱和甘汞电极的电极反应基于以下的氧化还原反应： Hg 2 2 + + 2 e − ↽ − − ⇀ 2 Hg ( l ) , with E Hg 2 2 + / Hg 0 = + 0.80 V {\displaystyle {\ce {Hg2^2+ + 2e^- <=> 2Hg(l)}},\qquad {\ce {with}}\quad E_{{\ce {Hg2^2+/Hg}}}^{0}=+0.80\ {\ce {V}}} Hg 2 Cl 2 + 2 e − ↽ − − ⇀ 2 Hg ( l ) + 2 Cl − , with E Hg 2 Cl 2 / Hg , Cl − 0 = + 0.27 V {\displaystyle {\ce {Hg2Cl2 + 2e^- <=> 2Hg(l) + 2Cl^-}},\qquad {\ce {with}}\quad E_{{\ce {Hg2Cl2/Hg, Cl-}}}^{0}=+0.27\ {\ce {V}}} 以上两半反应可以平衡为以下反应 Hg 2 2 + + 2 Cl − + 2 Hg ( l ) ↽ − − ⇀ Hg 2 Cl 2 ( s ) + 2 Hg ( l ) , with E Hg 2 Cl 2 / Hg 2 2 + , Cl − 0 = + 0.53 V {\displaystyle {\ce {Hg2^2+ + 2Cl^- + 2Hg(l) <=> Hg2Cl2(s) + 2Hg(l)}},\qquad {\ce {with}}\quad E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}=+0.53\ {\ce {V}}} . 以上反应可简化为氯化亚汞的沉淀反应，平衡常数为溶解积。 Hg 2 2 + + 2 Cl − ↽ − − ⇀ Hg 2 Cl 2 ( s ) , K s p = a Hg 2 2 + a Cl − 2 = [ Hg 2 2 + ] ⋅ [ Cl − ] 2 {\displaystyle {\ce {Hg2^2+ + 2Cl^- <=> Hg2Cl2(s)}},\qquad K_{sp}=a_{{\ce {Hg2^2+}}}a_{{\ce {Cl-}}}^{2}=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}} 这些半反应的能斯特方程为： { E 1 2 cathode = E Hg 2 2 + / Hg 0 − R T 2 F ln 1 a Hg 2 2 + in which E Hg 2 2 + / Hg 0 = + 0.80 V . E 1 2 anode = E Hg 2 Cl 2 / Hg , Cl − 0 − R T 2 F ln a Cl − 2 in which E Hg 2 Cl 2 / Hg , Cl − 0 = + 0.27 V . {\displaystyle {\begin{cases}E_{{\frac {1}{2}}{\ce {cathode}}}&=E_{{\ce {Hg_2^2+/Hg}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{a_{{\ce {Hg2^2+}}}}}\qquad &{\text{in which}}\quad E_{{\ce {Hg2^2+/Hg}}}^{0}=+0.80\ {\ce {V}}.\\E_{{\frac {1}{2}}{\ce {anode}}}&=E_{{\ce {Hg2Cl2/Hg,Cl-}}}^{0}-{\frac {RT}{2F}}\ln a_{{\ce {Cl-}}}^{2}\qquad &{\text{in which}}\quad E_{{\ce {Hg2Cl2/Hg, Cl-}}}^{0}=+0.27\ {\ce {V}}.\\\end{cases}}} 平衡反应的能斯特方程为： E cell = E 1 2 cathode − E 1 2 anode = E Hg 2 Cl 2 / Hg 2 2 + , Cl − 0 − R T 2 F ln 1 [ Hg 2 2 + ] ⋅ [ Cl − ] 2 = E Hg 2 Cl 2 / Hg 2 2 + , Cl − 0 − R T 2 F ln 1 K s p in which E Hg 2 Cl 2 / Hg 2 2 + , Cl − 0 = + 0.53 V {\displaystyle {\begin{aligned}E_{{\ce {cell}}}&=E_{{\frac {1}{2}}{\ce {cathode}}}-E_{{\frac {1}{2}}{\ce {anode}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{K_{sp}}}\qquad {\text{in which}}\quad E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}=+0.53\ {\ce {V}}\end{aligned}}} 其中E0是反应的标准电极电位， a Hg 2 2 + {\displaystyle {\ce {a_{{Hg_{2}}^{2+}}}}} 是亚汞离子的活度（每公升1 摩尔液体的活度为 1）。 在平衡时， Δ G = − n F E = 0 J / m o l {\displaystyle \Delta G=-nFE=0\mathrm {J/mol} } , 或等效地 E cell = 0 V {\displaystyle E_{\text{cell}}=0\ \mathrm {V} } . 这种等式使我们能够找到溶度积。 E cell = E Hg 2 Cl 2 / Hg 2 2 + , Cl − 0 − R T 2 F ln 1 [ Hg 2 2 + ] ⋅ [ Cl − ] 2 = + 0.53 + R T 2 F ln K s p = 0 V {\displaystyle E_{\text{cell}}=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}=+0.53+{\frac {RT}{2F}}\ln {K_{sp}}=0\ {\ce {V}}} ln K s p = − 0.53 ⋅ 2 F R T K s p = e − 0.53 ⋅ 2 F R T = [ Hg 2 2 + ] ⋅ [ Cl − ] 2 = 1.184 × 10 − 18 {\displaystyle {\begin{aligned}\ln {K_{sp}}&=-0.53\cdot {\frac {2F}{RT}}\\K_{sp}&=e^{-0.53\cdot {\frac {2F}{RT}}}\\&=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}=1.184\times 10^{-18}\end{aligned}}} 由于氯离子浓度高，汞离子浓度（ [ Hg 2 2 + ] {\displaystyle {\ce {[Hg2^2+]}}} ） 低。这降低了使用标准甘汞电极研究者发生汞中毒和其他汞问题的风险。 饱和甘汞电极电动势 Hg 2 Cl 2 + 2 e − ↽ − − ⇀ 2 Hg ( l ) + 2 Cl − , with E Hg 2 Cl 2 / Hg , Cl − 0 = + 0.27 V {\displaystyle {\ce {Hg2Cl2 + 2e- <=> 2Hg(l) + 2Cl^-}},\qquad {\ce {with}}\quad E_{{\ce {Hg2Cl2/Hg, Cl-}}}^{0}=+0.27\ {\ce {V}}} E 1 2 SCE = E Hg 2 Cl 2 / Hg , Cl − 0 − R T 2 F ln a Cl − 2 = + 0.27 − R T F ln [ Cl − ] . {\displaystyle {\begin{aligned}E_{{\frac {1}{2}}{\ce {SCE}}}&=E_{{\ce {Hg2Cl2/Hg,Cl-}}}^{0}-{\frac {RT}{2F}}\ln a_{{\ce {Cl-}}}^{2}\\&=+0.27-{\frac {RT}{F}}\ln[{\ce {Cl-}}].\end{aligned}}} 该方程中唯一的变量是氯阴离子的活性（或浓度）。但是由于内部溶液为饱和氯化钾溶液，这种活性是由氯化钾的溶解度决定的，即：342 g/L/74.5513 g/mol = 4.587 M (20 °C) 。此导致饱和甘汞电极在20 °C 下相对于标准氢电极具有+0.248 V的电位，而在25 °C 时饱和甘汞电极相对于标准氢电极具有+0.244 V的电位，但此值在氯离子浓度更高时数值会更高。 [1] 举例而言, 在25°C 下，3.5M氯化钾水溶液条件下的甘汞电极相较于标准氢电极电位为+0.250 V 。而在1M氯化钾水溶液条件下的甘汞电极相较于标准氢电极电位为+0.283 V。 应用 饱和甘汞电极可用于pH测量、循环伏安法和一般在水溶液中的电化学。 该电极和银/氯化银参考电极的工作方式相同。在两个电极中，金属离子的活性由金属盐的溶解度决定。 饱和甘汞电极含有汞，与银/氯化银参考电极中使用的银金属相比，汞对健康的危害要大得多。 参见 循环伏安法 标准氢电极 标准电极电位表 参比电极 参考资料 [1]Sawyer, Donald T.; Sobkowiak, Andrzej; Roberts, Julian L. Electrochemistry for Chemists 2nd. 1995: 192. ISBN 978-0-471-59468-0. Banus MG. A Design for a Saturated Calomel Electrode. Science. June 1941, 93 (2425): 601–602. PMID 17795970. doi:10.1126/science.93.2425.601-a.Wikiwand - on Seamless Wikipedia browsing. On steroids.
.![{\displaystyle {\ce {Hg2^2+ + 2Cl^- <=> Hg2Cl2(s)}},\qquad K_{sp}=a_{{\ce {Hg2^2+}}}a_{{\ce {Cl-}}}^{2}=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}}](//wikimedia.org/api/rest_v1/media/math/render/svg/4b28238442853c3c090271c8eea80ab866c4e9b4)
![{\displaystyle {\begin{aligned}E_{{\ce {cell}}}&=E_{{\frac {1}{2}}{\ce {cathode}}}-E_{{\frac {1}{2}}{\ce {anode}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{K_{sp}}}\qquad {\text{in which}}\quad E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}=+0.53\ {\ce {V}}\end{aligned}}}](//wikimedia.org/api/rest_v1/media/math/render/svg/d4a4f8dbd24a033aee568fc8a3ab5370e8f3cbc1)
是亚汞离子的活度（每公升1 摩尔液体的活度为 1）。
, 或等效地
.![{\displaystyle E_{\text{cell}}=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}=+0.53+{\frac {RT}{2F}}\ln {K_{sp}}=0\ {\ce {V}}}](//wikimedia.org/api/rest_v1/media/math/render/svg/bebe1c8e9f8b23c3dd7825182e7963a4412498d2)
![{\displaystyle {\begin{aligned}\ln {K_{sp}}&=-0.53\cdot {\frac {2F}{RT}}\\K_{sp}&=e^{-0.53\cdot {\frac {2F}{RT}}}\\&=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}=1.184\times 10^{-18}\end{aligned}}}](//wikimedia.org/api/rest_v1/media/math/render/svg/ea60e5aad090cbfda0da54ca12641cefe43286d9)
![{\displaystyle {\ce {[Hg2^2+]}}}](//wikimedia.org/api/rest_v1/media/math/render/svg/5f9cbd429afd369c10108e7f82ff4493a2a9f010)
） 低。这降低了使用标准甘汞电极研究者发生汞中毒和其他汞问题的风险。
![{\displaystyle {\ce {Hg2^2+ + 2Cl^- <=> Hg2Cl2(s)}},\qquad K_{sp}=a_{{\ce {Hg2^2+}}}a_{{\ce {Cl-}}}^{2}=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/4b28238442853c3c090271c8eea80ab866c4e9b4)
![{\displaystyle {\begin{aligned}E_{{\ce {cell}}}&=E_{{\frac {1}{2}}{\ce {cathode}}}-E_{{\frac {1}{2}}{\ce {anode}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}\\&=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{K_{sp}}}\qquad {\text{in which}}\quad E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}=+0.53\ {\ce {V}}\end{aligned}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/d4a4f8dbd24a033aee568fc8a3ab5370e8f3cbc1)
![{\displaystyle E_{\text{cell}}=E_{{\ce {Hg2Cl2/Hg2^2+, Cl-}}}^{0}-{\frac {RT}{2F}}\ln {\frac {1}{{\ce {[Hg2^2+]}}\cdot {\ce {[Cl^-]}}^{2}}}=+0.53+{\frac {RT}{2F}}\ln {K_{sp}}=0\ {\ce {V}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/bebe1c8e9f8b23c3dd7825182e7963a4412498d2)
![{\displaystyle {\begin{aligned}\ln {K_{sp}}&=-0.53\cdot {\frac {2F}{RT}}\\K_{sp}&=e^{-0.53\cdot {\frac {2F}{RT}}}\\&=[{\ce {Hg2^2+}}]\cdot [{\ce {Cl-}}]^{2}=1.184\times 10^{-18}\end{aligned}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/ea60e5aad090cbfda0da54ca12641cefe43286d9)
![{\displaystyle {\ce {[Hg2^2+]}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/5f9cbd429afd369c10108e7f82ff4493a2a9f010)
![{\displaystyle {\begin{aligned}E_{{\frac {1}{2}}{\ce {SCE}}}&=E_{{\ce {Hg2Cl2/Hg,Cl-}}}^{0}-{\frac {RT}{2F}}\ln a_{{\ce {Cl-}}}^{2}\\&=+0.27-{\frac {RT}{F}}\ln[{\ce {Cl-}}].\end{aligned}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/0deec05db0778c9b24c242c15ffee3031d8ed2ae)