有關 salt bridge

用Mg-Cu cell為例 (硫酸銅做電解質)
當電子由負極流向正極時(經電線)
正極下的電解質中的正離子會游上去接收電子(Cu(+) +電子 =Cu)
電解質中Cu(+)不停轉做Cu,所以電解質中的正離子減少.
正離子減少,所以會帶負電荷
濕左水的鹽橋中的正離子會流向電解質(因為帶負電荷)
另一方面.Mg失去電子變成Mg(+)
因為Mg(+)熔於電解質中.電解質中的正電荷上升,鹽橋上的負離子會走過去平衡佢
1.佢係提供正/負離子去平衡電荷
2.當Mg失去電子,Mg下面的電解質中的Mg(+)會增加.
因為(+)電荷增加,帶(-)電的電子便會被扯住.無法流去Cu果邊
最後反應結束....(鹽橋可以中和電荷令反應繼續)
希望冇打錯字　－.－



＊鹽橋只係一張紙.濕左d電解質例如(KNO3)

A salt bridge, in chemistry, is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. Salt bridge usually comes in two types: glass tube and filter paper.


Glass tube bridges
One type of salt bridges consists of U-shaped glass tubes filled with a relatively inert electrolyte, usually potassium chloride or sodium chloride. Agar is often used for gelification.

The conductivity of the glass tube bridges depends mostly on the concentration of the electrolyte solution. An increase in concentration below saturation increases conductivity. Beyond-saturation electrolyte content and narrow tube diameter may both lower conductivity.


Filter paper bridges
The other type of salt bridges consists of a filter paper, also soaked with a relatively inert electrolyte, usually potassium chloride or sodium chloride because they are chemically inert. No gelification agent is required as the filter paper provides a solid medium for conduction.

Conductivity of this kind of salt bridges depends on a number of factors: the concentration of the electrolyte solution, the texture of the filter paper and the absorbing ability of the filter paper. Generally smoother texture and higher absorbancy equates to higher conductivity.

A porous disk or other porous barrier between the two half-cells may be used instead of a salt bridge; however, they basically serve the same purpose.


Uses
As electrons leave one half of a galvanic cell and flow to the other, a difference in charge is established. If no salt bridge was used, this charge difference would prevent further flow of electrons. A salt bridges allows the flow of ions to maintain a balance in charge between the oxidation and reduction vessels while keeping the contents of each separate. With the charge difference balanced, electrons can flow once again, and the reduction and oxidation reactions can proceed. In general, keeping the two cells separate is preferable from the point of view of eliminating variables from an experiment. When no direct contact between electrolytes is allowed, there is no need to make allowance for possible interactions between ionic species.

The technique more specifically allows freedom in the choice of ions in solution. For instance, a mixture of two different cations in solution might result in the preferential reduction of the wrong one, for the purposes of the experiment. With a salt bridge, the desired cation is isolated in one vessel while the cation in the other vessel may be chosen to make the experiment easier, e.g. using a more soluble, or more stable salt of the anionic species.