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1、1Electrochemistry(3) Physical Chemistry2Physical ChemistryElectrolytic ConductivityElectrochemistrElectrochemistry yThe electric current I(16.46)*(16.47)*The electric current density jThe conductivity The reciprocal of conductivity (resistivity) (16.50)*(16.49)*3Physical ChemistryElectrolytic Conduc
2、tivityThe resistance R(16.46)*(16.54)The conductance G1 S=1 -1Siemensohm-1mhoElectrochemistrElectrochemistry y4Physical ChemistryMolar ConductivityThe conductivity of a solutiondepends on the number of ions presentThe molar conductivity mElectrochemistrElectrochemistry y(16.58)*The electrolytes stoi
3、chiometric molar concentration5Physical ChemistryH2SO4KOHKClMgSO4CH3COOH015510c/(moldm-3)20406080Conductivity vs. concentrationk/(Sm-1)0 vs. cStrong electrolytesFully ionized in solution: ionic solids, strong acids and bases The concentration of ions is proportional to the concentration of electroly
4、te added Weak electrolytesMgSO4CH3COOHNeutral electrolytesKClH2SO4KOHMolar ConductivityElectrochemistrElectrochemistry y(16.58)*6演示演示7400300200100m/(Scm2 mol-1)HClNaOHAgNO3CH3COOH0 0.5 1.0 1.5In an extensive series of measurements during 19th century, Friedrich KohlrauschAt low concentrationsThe inf
5、inite-dilute molar conductivityThe infinite-dilute molar conductivity of the cations and anionsLaw of the independent Law of the independent migration of ionsmigration of ionsMolar ConductivityPhysical ChemistryThe limiting molar conductivityElectrochemistrElectrochemistry y8演示演示9摩尔电导率与浓度的关系摩尔电导率与浓度
6、的关系 由于溶液中导电物质的量已给定，都为1mol，所以，当浓度降低时，粒子之间相互作用减弱，正、负离子迁移速率加快，溶液的摩尔电导率必定升高。但不同的电解质，摩尔电导率随浓度降低而升高的程度也大不相同。10ElectrochemistrElectrochemistry y11强电解质的强电解质的L Lm m与与c的关系的关系 随着浓度下降， 升高，通常当浓度降至 以下时， 与 之间呈线性关系。德国科学家Kohlrausch总结的经验式为： 是与电解质性质有关的常数。将直线外推至，得到无限稀释摩尔电导率 。Kohlrausch12 随着浓度下降， 也缓慢升高，但变化不大。当溶液很稀时， 与 不
7、呈线性关系，等稀到一定程度， 迅速升高，见 的 与 的关系曲线。弱电解质的 不能用外推法得到。强电解质的强电解质的Lm与与c的关系的关系13离子独立移动定律离子独立移动定律 德国科学家Kohlrausch 根据大量的实验数据，发现了一个规律：在无限稀释溶液中，每种离子独立移动，不受其它离子影响，电解质的无限稀释摩尔电导率可认为是两种离子无限稀释摩尔电导率之和： 这就称为Kohlrausch 离子独立移动定律。这样，弱电解质的 可以通过强电解质的 或从表值上查离子的 求得。14Physical ChemistryContributions of individual ions to the cu
8、rrentThe mobilities of ionsThe drift speedThe current density j+(16.60)noticedElectrochemistrElectrochemistry yViscous forceElectric field force15Physical ChemistryIf several kinds of ions are present in the solution The mobilities of ionsThe drift speed(16.61)The current density jB due to ion BThe
9、total current density jElectric mobilities of ionsIon mobilitiesElectrochemistrElectrochemistry y16Physical ChemistryElectric mobilities of ionsIons mobilityGiven solution, cB is fixedOhms lawconstant(16.62)*(16.63)(16.64)ElectrochemistrElectrochemistry y17Physical ChemistryElectric mobilities of io
10、ns(16.65)(16.64)(16.62)*ElectrochemistrElectrochemistry y18Physical ChemistryTransport numbersThe transport number tB Transference numbers(16.71)*(16.72)ElectrochemistrElectrochemistry y19Physical ChemistryTransport numbersTransference numbers(16.62)(16.73)ElectrochemistrElectrochemistry y20Physical
11、 ChemistryThe measurement of ionic mobilities and transport numbersMoving-boundary method (Fig. 16.23)Hittorf method (Fig. 16.25)ElectrochemistrElectrochemistry y21Physical ChemistryThe measurement of ionic mobilities and transport numbersMoving-boundary methodHittorf method ElectrochemistrElectroch
12、emistry y22迁移数的测定方法迁移数的测定方法1Hittorf 法法在Hittorf迁移管中装入已知浓度的电解质溶液，接通稳压直流电源，这时电极上有反应发生，正、负离子分别向阴、阳两极迁移。小心放出阴极部（或阳极部）溶液，称重并进行化学分析，根据输入的电量和极区浓度的变化，就可计算离子的迁移数。通电一段时间后，电极附近溶液浓度发生变化，中部基本不变。23界面移动法比较精确，也可用来测离子的淌度。根据毛细管的内径、液面移动的距离、溶液的浓度及通入的电量，可以计算离子迁移数。通电后， 向上面负极移动， 淌度比 小，随其后，使 界面向上移动。通电一段时间后， 移动到 位置，停止通电。 在界移
13、法的左侧管中先放入 溶液至 面，然后小心加入HCl溶液，使 面清晰可见。2.界面移动法界面移动法迁移数的测定方法迁移数的测定方法242.2.界面移界面移动法法设毛细管半径为 ，截面积 与 之间距离为 ，溶液体积 。 迁移的电量为 ，的迁移数为：在这个体积范围内， 迁移的数量为， 迁移数的测定方法迁移数的测定方法25Molar conductivities of ionsPhysical Chemistry(16.58)*(16.76)*(16.63)(16.77)(16.78)*(16.79)ElectrochemistrElectrochemistry y26Molar conductivi
14、ties of ionsPhysical Chemistry(16.77)(16.78)*(16.79)Strong electrolyte(16.80)Strong electrolyte, no ion pairs(16.81)ElectrochemistrElectrochemistry y27Applications of conductivityPhysical Chemistry(1) Titration: determine the endpoint from H3O+ is replaced by Na+More Na+ and OH-Indicators Electroche
15、mistrElectrochemistry y28演示演示29Applications of conductivityPhysical Chemistry(2) Purity of water: Purification of water(b) ionic exchange resins to remove anions and cations (deionized water)(a) KMnO4, KOH，remove CO2 and organic contaminants (doubly distilled water)(c) the resistivity of water 18 M (ultrapure water)ElectrochemistrElectrochemistry y30Dissociation constants of weak acids(3) Ionic equilibrium constantsAssociation constants for ion pair formation Applications of conductivityPhysical ChemistrySolubility-product constantsIonization constant of waterElectrochemistrElectrochemistry y
