Primary cells
Primary cells become dead after some time; as electrode reactions cannot be reversed, i.e., redox reaction takes place only once hence non-rechargeable. E.g. Dry cell, mercury cell Dry cell : It is a compact form of Lechlanche cell. In brief it can be summarised as: Anode Zinc Container Cathode Graphite rod surrounded by and carbon . Electrolyte Apaste of filled between two electrodes. Cell Potential 1.25 to 1.5 Volt Relation: At anode At cathode Here combine to give complex ion . This cell has a...
read moreFuel Cell
Fuel Cell is a galvanic cell in which fuel are etc. Electrodes: Porous carbon impregnated with gaseous catalyst like . Electrolyte: Aqueous KOH (concentration) Here fuels undergo combustion to give electric energy. E.g. : fuel cell: At anode: At cathode: Net reaction: Requirements: It should be compact, light, etc. Astronauts use fuel cell. It is pollution free, continuous source of high efficiency. Example: A 100 watt, 110 volt incandescent lamp is connected in series with an electrolyte cell containing cadmium sulphate...
read moreCorrosion
Corrosion is the attack of atmospheric gases on metal surface to change it into salts like oxides, carbonates, sulphides etc. It is a redox reaction and reverse of extraction of metals. E.g. Rusting of Iron: It can be explained according to electro-chemical theory as follows: Rust is hydrated ferric oxide, i.e., Factors increasing corrosion: (i) Presence of impurities in the metal (ii) Presence of electrolyte e. g. saline Water (iii) Presence of moisture or rainy season Prevention of...
read moreSecondary cell
Secondary cells are rechargeable by passing current as electrode reactions can be reversed e. g. lead storage battery, Ni-Cd storage cell. Lead storage battery: It contains 6 voltaic cells in a row . It is used in automobiles, invertors etc. Anode: Spongy lead Cathode: Grid of lead packed with Electrolyte: 38% by mass aqueosus solution of At anode: At cathode: Net reaction: is 2.04 volt During discharging is consumed. Nickel-Cadmium Batteries: Anode: Cd Cathode: Ni (III) compound supported on Ni or reactions: At anode:...
read moreCell Notation
Generally a cell is represented as follows: Certain notations have become fairly well known and are followed conventionally in connection with electrochemical cells. A half Cell such as Zn rod clipped in 0.1 M ion solution is represented by . The vertical line shows a solid phase. Thus the Daniell cell may be represented as: Where two vertical lines indicate the salt bridge. By convention, the anode of a cell is shown on the left in the cell notation. Example. Calculate the charge in coulomb on ion. Solution: Since ...
read moreNernst Equation
It describes the quantitative relationship between electrode potential and concentrations and temperature of the substance involved in the half cell reaction. Consider a simple general reaction: Nemst deduced the following mathematical expression for the above reaction: where, E = Electrode potential of the metal, = standard electrode potential, R = gas constant, T = temperature in K, F = Faraday constant , n = number of electrons involved in the half reaction, [M] = activity of metal in the solid phase or liquid phase and is...
read moreStandard Electrode Potential
It is potential difference developed between metal electrode and the ions of the solution of a molar concentration or 1 atm. pressure at 298 K [25°C]. It is denoted by . It is important to know that the absolute value of or or E cannot be determined as neither oxidation nor reduction reaction of half-cell occurs alone. Moreover we have to use a reference electrode i.e. an electrode with known value of electrode potential. The common reference electrode used is standard or normal hydrogen electrode which can work both as a cathode or an...
read moreElectrode Potential
When a metal rod is placed in a solution of metal ions the metal rod become oppositely charged to solution ions. As a result a potential develops between them. It is called electrode potential. E.g. Zn-rod becomes (-)vely charged in solution. In fact electrode potential is the tendency of a metal to loose or to gain electrons, i.e. It is measurement if tendency to get oxidize or to get reduced. It is denoted by E. The value of electrode potential depends upon: (A) Nature of electrode (B) Temperature (C) Concentration of ions in...
read moreSalt Bridge
Some of the importance of Salt bridge are listed below: (1). In Daniell cell electrons are released by anode and accepted by cathode. Therefore Zn changes into ion and changes into Cu. During this change there will be accumulation of charge near the two electrodes which prevents further flow of current. Due to this the electrochemical changes stop and current drops to zero. To prevent this, salt bridge is placed in between the two electrodes, In the presence of salt bridge, the charges flow towards the oppositely charged electrode. The...
read moreDaniel cell
The cells which produce electrical energy from chemical reactions are known as galvanic or voltaic cells. A galvanic cell in which one electrode is Zn plate in (or ion) solution and the other is Cu plate in ion) solution is called the Daniel cell. A schematic diagram of the cell is shown below: The two half reactions, I.e. At anode at cathode are made to take place simultaneously with the electron transfer occurring through an extemal conducting wire. The two solutions (i.e., ) are linked by an inverted U-shaped tube as salt bridge. The...
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