Copper coulometer

The Kupfercoulometer - like all coulometer - a historic unit, which allows electric charges and constant current intensities were determined in the DC circuit. It was used frequently in the period from about 1880 until after the middle of the 20th century. In particular Kupfercoulometer were used for higher current, for which the precise Silbercoulometer suitable size would have been very expensive. Like all coulometer has the Kupfercoulometer today hardly any practical significance, it is used only for training purposes.

The Kupfercoulometer contains at least two copper sheets or plates as electrodes, which are located in a slightly acidic copper (II ) sulfate solution. By the current flow through the series-connected cell, copper is dissolved in the positive electrode of copper (anode) and to the copper cathode, it comes to the separation of copper from the solution. From the determined with a scale change in mass of the dried copper electrodes, the total amount can be calculated of transmitted electric charge. At constant current, this is calculated from the known duration of electrolysis.

The electrolyte consisted mostly of 150 g of copper sulfate, 50 g of sulfuric acid, 50 g of ethanol and 1000 g of water.

Historical

The Kupfercoulometer, called in the 19th century copper voltameter was later than 1883 known in Germany, in England no later than 1886, the above mentioned electrolyte composition was recommended in 1893 in a paper by Felix Oettel. ; the electrolyte of copper sulphate CuSO4, H2SO4 sulfuric acid, ethanol C2H5OH and water H2O is therefore also called Oettelsche solution.

Variants

As a cathode, on which copper is deposited, and platinum sheet was used for accurate measurements. In particular, at high currents, it is advantageous to use a cathode plate of stainless steel, since this can support the weight of the deposited copper better, and since it is possible to remove the copper from the steel and weigh folded.

Reaction equations

The total concentration of the solution and the total mass of copper will not change.

Charge calculation

According to Faraday's law, the charge Q of the change in mass is proportional, and we have: