Question

Number of faradays of electricity required to liberate 12g of hydrogen is:
(a) 1
(b) 8
(c) 12
(d) 16

Answer 1

Hint: There is a relation between the number of moles and the charge flow involved in a reaction. They are directly proportional to each other. Faraday is the charge of 1 mole of electrons.

Complete step by step solution:
In order to know how much chemistry is taking place in an electrochemical cell, we can direct and measure the exact amount of electric current that flows through the cell. We need a means by which we can convert the charge into a number of electrons. For this use, Faraday’s constant is introduced. It has a symbol F and it is defined as the charge in coulombs of 1 mole of electrons.

In case of hydrogen‘s ionisation reaction,
\[{{H}_{2}}+2{{e}^{-}}\to 2{{H}^{+}}\]
Number of electrons involved is 2. For every mole of hydrogen, it produces two electrons. So, for every mole of electrons we have (number of moles of hydrogen x number of electrons per mole) equal to that much amount of faradays or coulombs of charge.
We know that the molecular weight of hydrogen is 2g per mol. So, the number of moles can be calculated by dividing the given mass which is 12g by the molecular mass 2g per mol.
Number of moles n= \[\dfrac{12}{2}=6\]
The ionisation hydrogen is as follows

\[{{H}_{2}}+2{{e}^{-}}\to 2{{H}^{+}}\]
From the above equation we get that for 6 moles of hydrogen 6x2=12 moles of electrons is needed. This corresponds to 12 faradays of electricity.
Thus, the number of faradays of electricity required for liberation of 12g of hydrogen is 12 and option (c) is correct.

Note: We should keep in mind that the electricity required or charge required depends on the number of moles involved in a reaction. In the equation we can see that there are two electrons required. So for n number of moles, n x 2 number of electrons are required.