Explain why KCl, NH4NO3 are suitable salt for a salt bridge?

Dear Student,

KCl and KNO3 are used to maintain the neutrality of the cells. The salt bridge provides cations and anions to replace the ions lost or produced in the two half cells. Therefore, it do not disturb the neutrality of the cell but infact helps to maintain it. For eg. if excess negative charge due to additional ions are produced, then the sufficient number of K+ ions migrate from the salt bridge to this half cell. This neutralizes the excess charge produced and thus makes it electrically neutral.
Salts like KCl,KNO 3, NH4NO3, etc. are used. NaCl is not used for this purpose because the transport number of Na+ is less than that of K+, thus during a long time of operation, NaCl causes an imbalance of ions in the electrochemical cell. Hence NaCl is not used.

Gelatin or agar-agar are used so as to keep the electrolyte in the semi-solid phase and thus prevents mixing. Any other jelly-like substance that can keep the electrolyte in the semi-solid phase can also be used but mostly gelatin and agar-agar are used. 


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