When two half cells are connected with each other, an electrochemical cell can be created. Salt bridge is used to connect those two half cells to keep the current flow from one cell to other cell. There are different types of electrochemical cells in the world and according to the requirement, right choice should be made. Electrochemical cell will give current when two half cells are connected with each other.
In this tutorial, we will study followings.
A reductant in equilibrium with an oxidant on a metal surface under standard conditions of temperature and pressure is known as an electrochemical half-cell. Here temperature should be kept at 298K and pressure at 1atm and all concentrations of ions at 1 mol dm-3. There are three possible types of half cells.
There are three types in electrochemical cells as below. These categorization is done by considering metals, ions and phases of matter.
A metal and its ions are at equilibrium at 1 atm pressure and 298k temperature. As the following figure, when Zinc metal is dissolved in a aqueous solution in mentioned physical conditions where Zn2+ ion concentration is 1.0 mol dm-3, its is defined as Zn|Zn2+ ion half cell.
There are two different ions which can independently function as oxidant and reductant. Electrode is made of a inactive anode such as Platinum (Pt). (Both the Oxidant and reductant must be available in the electrolyte).
A gas is adsorbed on to a Platinum plate and allow reaching to the equilibrium with its ions solution. Concentration of ions should be 1.0 mol dm-3 at 298K. Pressure of gaseous phase should be kept at 1 atm.
If any two different half cells are connected with each other through a salt bridge and a volt meter/an electric bulb and both half cells are kept under standard conditions. Then it is referred to as a standard electrochemical cell. If the metal plates of two half cells are connected to a bulb, it will produce light because generated current due to the potential difference of half cells is flown through the bulb. If they are connected through a voltmeter it will produce a deflection at the voltmeter. (Current could be produced by the electric cell)
Salt bridge is used to keep the current flow between electrochemical cells. Therefore, a good electrical conductivity should be in the salt bridge. The salt bridge takes the form of either,
The system (Half cell) with the algebraically lower reduction potential (Electrode potential) will be the negative terminal of the cell and this is known as the anode of the cell. Anode is the electrode where the oxidation takes place in an electrochemical cell.
The system (Electrode) with the algebraically higher reduction potential (Electrode Potential) will be the positive terminal of the cell and known as the cathode where the reduction takes place in an electrochemical cell.
Silver chloride is a precipitate. Therefore, it is a weak electrolyte which does not carry electricity properly as a strong electrolytes do.