Question

An electrolysis of an oxy tungsten complex ion using 1.20 A for 40 min produces 0.838 g of tungsten. What is the charge of tungsten in the material? (Atomic weight: W = 184)
A. 6
B. 3
C. 5
D. 1

Answer 1

Hint: Faraday’s law of electrolysis states that mass, m of any substance deposited through electrolysis is directly proportional to the current, $I$ passed in time T. Charge of any element is detected from the value of its equivalent weight.

Formula used: $m=ZIT$ , where m is mass, $I$ is current, T is time, Z is chemical equivalent obtained for a element by $\dfrac{molar\,mass}{ch\arg e}$.

Complete step-by-step answer: We are given an oxy tungsten complex ion from which an electricity of 1.20 A is passed, that decomposes it in 40 min into 0.838 of tungsten. Now we have to find the charge on the deposited tungsten material.
Charge n can be obtained by formula from Faraday's first law, $m=ZIT$, where Z is equivalent weight, E or electrochemical equivalent. Therefore,
 $\dfrac{W}{E}=\dfrac{IT}{F}$, E is the equivalent weight of tungsten as $\dfrac{molar\,mass}{ch\arg e}$ , putting the respective given values we will get,
$\dfrac{0.838}{\dfrac{184}{n}}=\dfrac{1.10\times 40\times 60}{F}$, rearranging to find charge, n,
n = $\dfrac{184\times 1.10\times 40\times 60}{0.838\times 96500}$ (the value of faraday's constant, 1 F = 96500)
n = 6

Hence, the charge on the deposited tungsten material is +6. So option A is correct.

Note: The time 40 min is converted into seconds by multiplying it into 60 seconds. Equivalent weight of any element is the value of its molar mass upon charge. Tungsten is the strongest metal, which is used in making filaments of bulbs, due to its high melting point.