The amount of any substance deposited or dissolved at a particular electrode is proportional to the quantity of electricity passed i. Electrochemical equivalent is the mass of substance deposited in grams either by passing one coulomb of charge or by passing one ampere of current for one second.
Let E be the equivalent mass of a substance deposited at any electrode. Since coulombs of charge is required to deposit E g of substance, therefore one coulomb of charge would deposit g, which is nothing but electrochemical equivalent. An important use of this equation lies in its application for the measurement of quantity of electricity or of current strength or the time taken for discharge of an ion or cathode area, or thickness of deposited layer or density of metal deposited.
The amounts of different substances deposited or dissolved by the same quantity of electricity are proportional to their chemical equivalent weights. This means that if the quantity of charge passed through cells connected in series is same, the amount of substance deposited at various electrodes in terms of equivalents would also be same.
Another way of stating this law is that the same quantity of electricity will produce chemically equivalent quantities of all substances resulting from the process.
Moreover, since coulombs will yield one equivalent of silver, a direct consequence of Faraday's second law is that during electrolysis coulombs of electricity will yield one equivalent of any substance.
For example, consider the given reactions at two different cathodes in two different electrolytic cells connected in series. Let us assume x moles of electrons is passed through the two cells. The mass of Ag and Cu deposited are x and We can see that and Less than one-half a mole of electrons was involved and less than one-half a mole of silver was produced.
In one application, a 0. How long would it take to deposit the layer of chromium if the current was The density of chromium metal is 7. This problem brings in a number of topics covered earlier.
An outline of what needs to be done is:. Cubic centimeters were used because they match the volume unit used for the density. The amount of Cr is then. Since the solution contains chromium III ions, 3 moles of electrons are required per mole of Cr. The total charge is then. Check your answer: In a long problem like this, a single check is probably not enough. Each of the steps gives a reasonable number, so things are probably correct. Pay careful attention to unit conversions and the stoichiometry.
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Don't want to keep filling in name and email whenever you want to comment? Hydrogen peroxide, H 2 O 2 , can be manufactured by electrolysis of cold concentrated sulfuric acid. The reaction at the anode is. When the resultant peroxydisulfuric acid, H 2 S 2 O 8 , is boiled at reduced pressure, it decomposes:. Calculate the mass of hydrogen peroxide produced if a current of 0. Knowing this we easily calculate the amount of electrons, n e —.
The road map to describe this logic is as follows:. Solution According to Eq.
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