PRIMARY VOLTAIC CELLS

Primary Voltaic Cells 21-22 Dry Cells Seeondary Voltaic Cells... 

Primary voltaic cell A voltaic cell that cannot be recharged no further chemical reaction is possible once the reactants are... 

What does voltage measure How does it vary with time in a primary voltaic cell Why ... 

Distinguish among (a) primary voltaic cells, (b) secondary voltaic cells, and (c) fuel cells. 

Daniell cell A type of primary voltaic cell with a copper positive electrode and a negative electrode of a zinc amalgam. The zinc-amalgam electrode is placed in an electrolyte of dilute sulphuric acid or zinc sulphate solution in a porous pot, which stands in a solution of copper sulphate in which the copper electrode is immersed. While the reaction takes place ions move through the porous pot, but when it is not in use the cell should be dismantled to prevent the diffusion of one electrolyte into the other. The e.m.f. of the cell is 1.08 volts with sulphmic acid and 1.10 volts with zinc sulphate. It was invented in 1836 by the British chemist John Daniell (1790-1845). 

Leclanche cell A primary voltaic cell consisting of a carbon rod (the anode) and a zinc rod (the cathode) dipping into an electrolyte of a 10-20% solution of ammonium chloride. Polarization is prevented by using a mixture of manganese dioxide mixed with crashed carbon, held in contact with the anode by means ofaporousbagorpot this reacts with the hydrogen produced. This wet form of the cell, devised in 1867 by Georges Leclanchfi (1839-82), has an e.m.f. of about... 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

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