Question

A silver cup is plated with silver by passing 905 coulombs of electricity, the amount of silver deposited is:
A. 9.89g
B. 107.87g
C. 1.0787g
D. 1.002g

Answer 1

Hint: The coulomb is defined as the quantity which is used to measure electricity. If the 1 amp of current flows for time 1 second then the electricity that would have been passed is equal to 1 coulomb. The question is to be solved by using the concept of Faraday's first law.

Complete step by step answer:
Faraday's first law says that the amount of substance which has been produced at the electrode during the process of electrolysis is directly proportional to the electricity that has been passed through the electrolyte. The formula which we will be using to calculate the quantity for silver is the following:
$${\text{W = }}\dfrac{{{\text{QZ}}}}{{{\text{96500}}}}$$
Here W is the amount of the substance that has been deposited
Z is the electro chemical equivalent of the substance
Q is the quantity of the electricity that has been passed.
So the equivalent weight of silver will be:
Equivalent weight =$$\dfrac{{{\text{Atomic Mass}}}}{{{\text{valency}}}}{\text{ = }}\dfrac{{{\text{108}}}}{{\text{1}}}{\text{ = 108eqmo}}{{\text{l}}^{{\text{ - 1}}}}$$
The Q is 965 coulombs.
Now substituting the values in formula we get,
$${\text{W = }}\dfrac{{965 \times 107.87}}{{{\text{96500}}}} = 1.0787g$$

So, the correct answer is Option C.

Note: The Faradays has given us two laws out of which one I have stated above. Now the Faraday second law states that masses of the two different substances liberated or dissolved at the same amount of the electricity passed will be directly proportional to their equivalent weight. The formula for calculating the electricity passed we need to multiply the current by the time given.