Question

The density and eq. wt. of a metal are $10.5g{cm}^{-3}$ and $100$, respectively. The time required for a current of $3$ amp to deposit a $0.005mm$ thick layer of the same metal on an area of $80{cm}^2$ is closest to:

• A. $120s$
• B. $135s$
• C. $67.5s$
• D. $270s$

Answer 1

The correct option is B $135s$

Volume $=80c{m}^2\times 0.005mm\times 0.1cm/mm=0.04c{m}^3$

The density is 10.5 $g/c{m}^3$
The mass of metal is $10.5g/c{m}^3\times 0.04c{m}^3=0.42g$

The equivalent weight of metal is 100 g/ g eq
The number of equivalents of metal are

$=\frac{0.42g}{100g/geq}=0.0042geq$
Number of moles of electrons $=$ number of gram equivalents $=0.0042$.

$0.0042=\frac{I\left(A\right)\times t\left(s\right)}{96500}$

$0.0042=\frac{3A\times t\left(s\right)}{96500}$

$t\left(s\right)=\frac{0.0042\times 96500}{3}$

$t\left(s\right)=135$ s