Video. Preparing a salt bridge from a peice of string.
A salt bridge allows the flow of charged ions between two half-cells, but prevents diffusional mixing of the two different metal salt solutions. Many things can be used as a salt bridge: a piece of string, cotton, or filter paper soaked in an electrolyte solution or an electrolyte solution in a gel such as agar. Occasionally, fritted glass (porous glass), though not a salt bridge, is used to connect two half-cells.
Soaking string, cotton, or paper in an electrolyte solution: Obtain a peice of material that is large enough to reach between two half-cells. Place the material is an electrolyte solution (a KNO3 solution is a common electrolyte solution) for a few seconds or until the material is saturated with the solution. Carefully remove the material from the electrolyte solution and eliminate any excess electrolyte solution (the material should be wetted, but not dripping).
Preparing a gel to function as a bridge: Gel material may be suspended in an electrolyte solution, and depending on the type of material used, the suspension may be treated with a buffered solution or heated. The viscous gel is then allowed to set either in a glass tube or on a glass plate. Once the gel has set (the gel appears to be elastic, and not fluid), it is ready for use.
