Science, Tech, Math › Science Salt Bridge Definition Share Flipboard Email Print A salt bridge connects the oxidation and reduction half reactions in a galvanic cell, such as a Daniell cell. Tinux/Wikimedia Commons/CC BY-SA 3.0 Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 2019 A salt bridge is a connection containing a weak electrolyte between the oxidation and reduction half-cells in a galvanic cell (e.g., voltaic cell, Daniell cell). Its purpose is to keep the electrochemical reaction from reaching equilibrium too quickly. If a cell is constructed without a salt bridge, one solution would quickly accumulate positive charge while the other would accumulate negative charge. This would halt the reaction and thus the generation of electricity. Types of Salt Bridges The two main types of salt bridges are a glass tube and a piece of filter paper: Glass Tube Bridge: This is a U-shaped glass tube filled with an electrolyte, such as sodium chloride, potassium chloride, or potassium nitrate. The electrolyte needs to be relatively unreactive with other chemicals in the cell and have cations and anions with similar migratory speed (comparable ion charge and molecular weight). Because a salt solution could easy diffuse into the cell, the electrolyte is often held in a gel, such as agar-agar. The concentration of the salt solution is the biggest factor in conductivity. The diameter of the tube also has an effect. Lowering the concentration of the electrolyte or narrowing the glass tube lowers conductivity. Filter Paper Bridge: Another common type of salt bridge consists of filter paper or another porous material soaked in an electrolyte (usually sodium chloride or potassium chloride). In this bridge, conductivity is affected by electrolyte concentration, porosity of the filter paper, and the roughness of the paper. A smooth, absorbent paper yields higher conductivity than rough paper with low absorbency. Reference Hogendoorn, Bob (2010). Heinemann Chemistry Enhanced (2). Melbourne, Australia: Pearson Australia. p. 416.