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Chromium plating is applied by electroly...

Chromium plating is applied by electrolysis to objects suspended in a dichlromate solution , according to following `(` unbalanced `)` hald reaction `:`
`Cr_(2)O_(7)^(2-)(aq) +e^(-) +H^(o+)(aq) rarr Cr(s)+H_(2)O(l)`
How many hours would it take to apply a chromium plating of thickness `2.0xx10^(-2)mm` to a car bumper of suface area `0.25m^(2)` in an electrolysis cell carrying a current of `75.0A?`
`[` Density of chromium is `7.19g cm^(-3)]`

A

`2.2h`

B

`1.5h`

C

`3.0h`

D

`0.2`

Text Solution

Verified by Experts

The correct Answer is:
B
Volume of be covered `= (0.25xx1^(4) cm^(2)) xx(2xx10^(-3)cm)= 5cm^(3)`
`Rightarrow` Mass of Cr to be deposited `= 5xx7.19 gm = 3.5 . 95 gm equiv (35.95)/(52) ("moles") =0.69 ("moles")`
`Cr_(2) O_(7)^(2-) + 14H^(+) + 12e^(-) rightarrow 2Cr + 7H_(2)O`
Now , 2 moles Cr deposited `equiv12F` electricity
`Rightarrow (2xx0.2 ) xx15 = (1xxM+(KOH)xx20 Rightarrow M_(KOH) = M_(KOH) = 0.3M`
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