User:XXryoul/Salt Bridge

Section - Introduction
In electrochemistry, a salt bridge or ion bridge is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. It maintains electrical neutrality within the internal circuit. If no salt bridge were present, the solution in one-half cell would accumulate a negative charge and the solution in the other half cell would accumulate a positive charge as the reaction proceeded, quickly preventing further reaction, and hence the production of electricity. Salt bridges usually come in two types: glass tubes and filter paper.

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- definition of salt bridge in electrochemistry

- the function of salt bridge

- types of salt bridge

- disadvantages of not having salt bridge

- add more references

- how to set up a salt bridge in electrochemistry

Article body
In electrochemistry, a salt bridge or ion bridge is an essential laboratory device which was discovered over 100 years ago. It contains an electrolyte solution, typically an inert solution, used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. In short, it functions as a link connecting the anode and cathode half-cells within an electrochemical cell. It also maintains the electrical neutrality within the internal circuit and stabilize the junction potential between the solutions in the half-cells. Additionally, it serves to minimize cross-contamination between the two half cells and helps in concentrating our focus on unfolding the funtion of working electrodes of the half cells.

A salt bridge typically consists of tubes filled with an electrolyte solution. These tubes often have diaphragms such as glass frits, at their ends to help contain the solution within the tubes and prevent excessive mixing with the surrounding environment. When setting up a salt bridge between different solvents of half-cells, it is crucial to ensure that the electrolyte used in the bridge is soluble in both solutions and does not interact with any species present in either solutions.

There are several types of salt bridges: glass tube bridges (traditional KCl- type salt bridge and ionic liquid salt bridge), filter paper bridges, porous frit salt bridges, fumed-silica, and agar gel salt bridges.

Glass tube bridges[edit]
One type of salt bridge consists of a U-shaped glass tube filled with a relatively inert electrolyte. It is usually a combination of potassium or ammonium cations and chloride or nitrate anions, which have similar mobility in solution. The combination is chosen which does not react with any of the chemicals used in the cell. The electrolyte is often gelified with agar-agar to help prevent the intermixing of fluids that might otherwise occur.

The conductivity of a glass tube bridge depends mostly on the concentration of the electrolyte solution. At concentrations below saturation, an increase in concentration increases conductivity. Beyond-saturation electrolyte content and narrow tube diameter may both lower conductivity.

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Glass tube salt bridges commonly consist of U-shaped Vycor tubes filled with a relatively inert electrolyte. The electrolyte solution usually comprises a combination of cations, such as ammonium and potassium, and anions, including chloride and nitrate, which have similar mobility. Traditionally, concentrated aqueous potassium chloride (KCl) solution has been used for decades to neutralize the liquid-junction potential. When comparing other salt solutions such as potassium bromide and potassium iodide to potassium chloride, potassium chloride is the most efficient in nullifying the junction potential. Yet, the effectiveness of this salt bridge decreases as the ionic strength of the sample solution increases.

Due to the numerous drawbacks of KCl-type salt bridges, ionic liquid salt bridges (ILSB) have been utilized to address the potentiometry issues arising from KCl-type salt bridges in electrochemical cells. ILSBs demonstrate efficient performance in aqueous solutions of hydrophilic electrolytes. This is because ionic liquids do not mix with water (they are immiscible), rendering them suitable as salt bridges for aqueous solutions. Additionally, they are chemically inert and highly stable in water.

To set up a glass tube salt bridge, the U-shaped vycor tube is constructed to contain any suitable electrolyte solution. The ends of the tube will be covered nomarlly by glass frits, a porous material, to prevent excessive mixing between the solutions.

The conductivity of a glass tube bridge depends mostly on the concentration of the electrolyte solution. At concentrations below saturation, an increase in concentration increases conductivity. Beyond-saturation electrolyte content and narrow tube diameter may both lower conductivity.

Glass tube bridges[edit]
One type of salt bridge consists of a U-shaped glass tube filled with a relatively inert electrolyte.[2] It is usually a combination of potassium or ammonium cations and chloride or nitrate anions, which have similar mobility in solution. The combination is chosen which does not react with any of the chemicals used in the cell.[3] The electrolyte is often gelified with agar-agar to help prevent the intermixing of fluids that might otherwise occur.

The conductivity of a glass tube bridge depends mostly on the concentration of the electrolyte solution. At concentrations below saturation, an increase in concentration increases conductivity. Beyond-saturation electrolyte content and narrow tube diameter may both lower conductivity.

Filter paper bridges[edit]
Porous paper such as filter paper may be used as a salt bridge if soaked in an appropriate electrolyte such as the electrolytes used in glass tube bridges. No gelification agent is required as the filter paper provides a solid medium for conduction.

The conductivity of this kind of salt bridge depends on a number of factors: the concentration of the electrolyte solution, the texture of the paper, and the absorbing ability of the paper. Generally, smoother texture and higher absorbency equate to higher conductivity.

A porous disk or other porous barriers between the two half-cells may be used instead of a salt bridge; these allow ions to pass between the two solutions while preventing bulk mixing of the solutions.

Lead
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- expand more on what is glass tube bridge is

- how to set up glass tube salt bridges

- advantages/ disadvantages of using filter paper

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Filter paper bridges[edit]
Porous paper such as filter paper may be used as a salt bridge if soaked in an appropriate electrolyte such as the electrolytes used in glass tube bridges. No gelification agent is required as the filter paper provides a solid medium for conduction.

The conductivity of this kind of salt bridge depends on a number of factors: the concentration of the electrolyte solution, the texture of the paper, and the absorbing ability of the paper. Generally, smoother texture and higher absorbency equate to higher conductivity.

To set up this type of salt bridge, laboratory filter paper can be used and rolled to form a shape that connects the two half-cells, typically rolled into a cylindrical shape. The rolled filter paper is then soaked in an appropriate inert salt solution. A straw can be used to shape the rolled filter paper into a U-shaped tube, providing mechanical strength to the soaked filter paper. This filter paper can now be used to act as a salt bridge and connect the two half-cells.

While filter paper salt bridges are inexpensive and easily accessible, one disadvantage of not using a straw to provide mechanical strength is that a new rolled and soaked filter paper must be used for each experiment.

Charcoal salt bridges[edit]
The charcoal salt bridge, discovered in 2019, is considered an excellent option for a porous junction for the reference electrode in an alkaline solution. A porous junction serves as a salt bridge between the two half-cells of reference and electrolyte solutions. Other materials used for porous junctions, such as glass, Teflon, and agar gel, have their own benefits but also some significant drawbacks such as high cost and high risk of contamination.

Therefore, the advantages of using charcoal as frits include its low cost and easy accessibility, as charcoal can be sourced from porous carbon materials. Despite being fragile, charcoal facilitates efficient ion transfer due to its highly porous structure.