F.5 Chem Electrolysis

2011-02-08 6:50 pm

我有兩樣野唔係幾明:(

1)electroplating of Fe咪會use iron object as cathode and the plating metal as anode嘅~跟住個electrolyte就係CuSO4(aq)丫嘛~咁我明個Cu2+係preferentially discharged at cathode,,but why 個iron object唔會有displacement reaction跟住dissolve to the solution as Fe2+??

2)purification of Cu果時係用CuSO4(aq)做electrolyte架嘛,,咁但係Ag係高過SO4 2- in the e.c.s.架喎,,點解佢唔會discharge反而就係solid咁deposit at the bottom呢??

thz:D

更新1:

之但係個impure copper入面都有d metal higher than Cu in the e.c.s.架喎,,例如Zn咁啦,,,咁點解Zn discharge完Cu會discharge,,但係Cu discharge完Ag就唔會discharge??

更新2:

sor呀,,可能我問得唔清楚,,其實我係想問咁當所有Cu都discharge完,,咁Ag就會開始discharge啦,,咁之後d Ag+咪會preferentailly discharged than Cu2+囉,,咁個pure copper咪會coated with a layer of Ag?咁咪即係purify唔到個Cu囉?? 定係其實Cu discharge完Ag都唔會discharge??

更新3:

係唔係即係Ag之前仲有其他metal同OH-要溶,,輪都未輪到佢就趺左出嚟??

回答 (1)

[匿名]

2011-02-08 7:25 pm

✔ 最佳答案

1.)因為在athode的iron object連到負極,而不斷收到來自電源的電子,所以iron object本身不會loss electron,因而不會dissolve to the solution as Fe2+

2)因為在purification of Cu時,anode也會copper,Cu的reducing power 高過Ag,SO4 2-,和水ionize 出來的OH-, 所以在通電時會是Cu dissolve,而Ag就會deposit at the bottom

2011-02-08 12:53:50 補充：
如果impure copper中有Zn之類比Cu更reactive的metal,這些metal都會discharge and dissolve,但因為這些metal產生出來的ion無Cu2+那麼容易discharge,所以不會deposit上Cu cathode上

2011-02-08 13:00:42 補充：
至於作為雜質的Ag,因為electrode中其他金屬已經dissolve,但Ag無溶,所以會跌出來,而且Ag的reducing power比ionize 出來的OH-低,所以Ag不會discharge

2011-02-08 13:27:23 補充：
可以這樣說,順帶一提,OH-不是溶,而是變成O2釋出

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