Question

The units of electrochemical equivalent is:
(A) gram coulomb
(B) gram $A^{-1}{s}^{{}^{-1}}$
(C) gram $A{s}^{-1}$
(D) gram $A^{-1}s$

Answer 1

Hint: From the definition of electrochemical equivalent we would be able to formulate an equation and this equation will be in terms of coulombs. By finding out the relationship between coulombs and ampere we would be able to find the unit of electrochemical equivalent.

Complete step by step solution:
-Let's start with the concept of electrochemical equivalent. The electrochemical equivalent of a substance can be defined as the mass of that substance liberated by the passage of one coulomb of electron flows Or when a current of one Ampere is passed for one second, the mass of the substance deposited to one of the electrodes, that is the quantity of electricity of one Coulomb is passed can also be described as electrochemical equivalent.
-Hence by the above definition we can write the formula for finding electrochemical equivalent(Z) as follows
$Z={\displaystyle \frac{M}{q}}$
Where Z is the electrochemical equivalent
M is the mass of the substance
q is the charge passed.
-We know that the unit of mass can be taken in grams and charge in coulombs. Therefore, the unit of electrochemical equivalent will be gram per coulomb. Hence option (A) can be excluded as it is given as gram coulombs.
-Now we need to find the relationship between ampere and coulomb in order to get the unit of electrochemical equivalent in terms of amperes. As we know, coulomb is the magnitude of charge flows in a specific time and ampere (A) is the rate of the number of charge flows per second(s). Mathematically it can be represented as follows
$1ampere={\displaystyle \frac{1coulomb}{1second}}$
Therefore, coulomb = $As$
Substituting this in gram per coulomb we get the unit of electrochemical equivalent as gram $A^{-1}{s}^{-1}$

Therefore, the answer is option (B).

Note: Do not confuse electrochemical equivalent with chemical equivalent. The chemical equivalent can be described as the weight of one gram of substance which can displace with or combine with one gram of hydrogen and it can be found by dividing the weight of the substance by valency whereas the electrochemical equivalent is the ratio between the weight and charge passed.