Salt bridge is a connection that exists between the positive electrode and the negative electrode of a battery.. It can consist of a U-shaped glass tube filled with a concentrated aqueous solution of a highly soluble salt; could be potassium chloride (KCl(here)), ammonium nitrate (NH4AT THE3(aq)), sodium nitrate (NaNO3(aq)) or potassium nitrate (KNO3(aq)).
At the ends of this tube, place it with cotton, glass wool or agar (gelatinous substance removal of red algae that is used in food and as a culture medium in laboratories bacteriological).
Agar-agar, a substance taken from red algae (image in the center), which is used to produce food, a culture medium and is used in the salt bridge.
To understand the need to implant a salt bridge between the electrodes of a battery, look at the image below and recall some battery concepts.
In a cell there is the anode or negative pole from which electrons migrate towards the cathode, or positive pole. In the case shown, the anode is metallic zinc (from the plate - Zn
0) and the cathode, the copper cations (Cu2+). Over time, this electron transfer will cause both solutions to lose their electrical neutrality, because there will be an excess of ions, making the solutions unstable and interrupting the functioning of the battery.Do not stop now... There's more after the advertising ;)
Thus, to eliminate these excesses, a saline bridge or a porous porcelain plate is used, which allows the migration of ions from one solution to another. In this way, the ions remain in balance and the battery continues to function.
In the salt bridge of the stack mentioned above, we have the migration of chloride ions (Cl1-(here)) for the zinc electrode because of the appearance of zinc ion (Zn2+(here)); and potassium ions (K1+(here)) are transferred to the copper electrode, which is less reactive than zinc, to neutralize excess negative charges (SO42-(here)) which occurs due to the decrease of Cu ions2+(here) in solution.
By Jennifer Fogaça
Graduated in Chemistry
Brazil School Team
Physicochemical - Chemistry - Brazil School
Would you like to reference this text in a school or academic work? Look:
FOGAÇA, Jennifer Rocha Vargas. "Function of the salt bridge in a pile"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/funcao-ponte-salina-uma-pilha.htm. Accessed on June 28, 2021.
