物理化學(xué)英文課件：Electrochemistry-3

1、1Electrochemistry(3) Physical Chemistry2Physical ChemistryElectrolytic ConductivityElectrochemistryThe electric current I(16.46)*(16.47)*The electric current density jThe conductivity The reciprocal of conductivity (resistivity) (16.50)*(16.49)*3Physical ChemistryElectrolytic ConductivityThe resista

2、nce R(16.46)*(16.54)The conductance G1 S=1 -1Siemensohm-1mhoElectrochemistry4Physical ChemistryMolar ConductivityThe conductivity of a solutiondepends on the number of ions presentThe molar conductivity mElectrochemistry(16.58)*The electrolytes stoichiometric molar concentration5Physical ChemistryH2

3、SO4KOHKClMgSO4CH3COOH015510c/(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 electrolyte added Weak electrolytesMgSO4CH3COOHNeutral elect

4、rolytesKClH2SO4KOHMolar ConductivityElectrochemistry(16.58)*6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 infinite-dilute molar conductivityThe infinite-dilute molar conductivity

5、of the cations and anionsLaw of the independent migration of ionsMolar ConductivityPhysical ChemistryThe limiting molar conductivityElectrochemistry8演示9摩爾電導(dǎo)率與濃度的關(guān)系 由于溶液中導(dǎo)電物質(zhì)的量已給定，都為1mol，所以，當(dāng)濃度降低時(shí)，粒子之間相互作用減弱，正、負(fù)離子遷移速率加快，溶液的摩爾電導(dǎo)率必定升高。但不同的電解質(zhì)，摩爾電導(dǎo)率隨濃度降低而升高的程度也大不相同。10Electrochemistry11強(qiáng)電解質(zhì)的Lm與c的關(guān)系 隨著濃度下

6、降， 升高，通常當(dāng)濃度降至 以下時(shí)， 與 之間呈線性關(guān)系。德國(guó)科學(xué)家Kohlrausch總結(jié)的經(jīng)驗(yàn)式為： 是與電解質(zhì)性質(zhì)有關(guān)的常數(shù)。將直線外推至，得到無限稀釋摩爾電導(dǎo)率 。Kohlrausch12 隨著濃度下降， 也緩慢升高，但變化不大。當(dāng)溶液很稀時(shí)， 與 不呈線性關(guān)系，等稀到一定程度， 迅速升高，見 的 與 的關(guān)系曲線。弱電解質(zhì)的 不能用外推法得到。強(qiáng)電解質(zhì)的Lm與c的關(guān)系13離子獨(dú)立移動(dòng)定律 德國(guó)科學(xué)家Kohlrausch 根據(jù)大量的實(shí)驗(yàn)數(shù)據(jù)，發(fā)現(xiàn)了一個(gè)規(guī)律：在無限稀釋溶液中，每種離子獨(dú)立移動(dòng)，不受其它離子影響，電解質(zhì)的無限稀釋摩爾電導(dǎo)率可認(rèn)為是兩種離子無限稀釋摩爾電導(dǎo)率之和： 這就稱為K

7、ohlrausch 離子獨(dú)立移動(dòng)定律。這樣，弱電解質(zhì)的 可以通過強(qiáng)電解質(zhì)的 或從表值上查離子的 求得。14Physical ChemistryContributions of individual ions to the currentThe mobilities of ionsThe drift speedThe current density j+(16.60)noticedElectrochemistryViscous forceElectric field force15Physical ChemistryIf several kinds of ions are present in

8、the solution The mobilities of ionsThe drift speed(16.61)The current density jB due to ion BThe total current density jElectric mobilities of ionsIon mobilitiesElectrochemistry16Physical ChemistryElectric mobilities of ionsIons mobilityGiven solution, cB is fixedOhms lawconstant(16.62)*(16.63)(16.64

9、)Electrochemistry17Physical ChemistryElectric mobilities of ions(16.65)(16.64)(16.62)*Electrochemistry18Physical ChemistryTransport numbersThe transport number tB Transference numbers(16.71)*(16.72)Electrochemistry19Physical ChemistryTransport numbersTransference numbers(16.62)(16.73)Electrochemistr

10、y20Physical ChemistryThe measurement of ionic mobilities and transport numbersMoving-boundary method (Fig. 16.23)Hittorf method (Fig. 16.25)Electrochemistry21Physical ChemistryThe measurement of ionic mobilities and transport numbersMoving-boundary methodHittorf method Electrochemistry22遷移數(shù)的測(cè)定方法1Hit

11、torf 法在Hittorf遷移管中裝入已知濃度的電解質(zhì)溶液，接通穩(wěn)壓直流電源，這時(shí)電極上有反應(yīng)發(fā)生，正、負(fù)離子分別向陰、陽(yáng)兩極遷移。小心放出陰極部（或陽(yáng)極部）溶液，稱重并進(jìn)行化學(xué)分析，根據(jù)輸入的電量和極區(qū)濃度的變化，就可計(jì)算離子的遷移數(shù)。通電一段時(shí)間后，電極附近溶液濃度發(fā)生變化，中部基本不變。23界面移動(dòng)法比較精確，也可用來測(cè)離子的淌度。根據(jù)毛細(xì)管的內(nèi)徑、液面移動(dòng)的距離、溶液的濃度及通入的電量，可以計(jì)算離子遷移數(shù)。通電后， 向上面負(fù)極移動(dòng)， 淌度比 小，隨其后，使 界面向上移動(dòng)。通電一段時(shí)間后， 移動(dòng)到 位置，停止通電。 在界移法的左側(cè)管中先放入 溶液至 面，然后小心加入HCl溶液，使 面清

12、晰可見。2.界面移動(dòng)法遷移數(shù)的測(cè)定方法242.界面移動(dòng)法設(shè)毛細(xì)管半徑為 ，截面積 與 之間距離為 ，溶液體積 。 遷移的電量為 ，的遷移數(shù)為：在這個(gè)體積范圍內(nèi)， 遷移的數(shù)量為， 遷移數(shù)的測(cè)定方法25Molar conductivities of ionsPhysical Chemistry(16.58)*(16.76)*(16.63)(16.77)(16.78)*(16.79)Electrochemistry26Molar conductivities of ionsPhysical Chemistry(16.77)(16.78)*(16.79)Strong electrolyte(16.80

13、)Strong electrolyte, no ion pairs(16.81)Electrochemistry27Applications of conductivityPhysical Chemistry(1) Titration: determine the endpoint from H3O+ is replaced by Na+More Na+ and OH-Indicators Electrochemistry28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)Electrochemistry30Dissociation