Chromium plating is applied by electrolysis to objects suspended in a dichromate solution, according to the following half reaction : C r 2 O 7 2 − ( a q ) + H + ( a q ) + e − → 2 C r ( s ) + H 2

Question

Chromium plating is applied by electrolysis to objects suspended in a dichromate solution, according to the following half reaction :

$C r_{2} O_{7}^{2 -} (a q) + H^{+} (a q) + e^{-} \to 2 C r (s) + H_{2} O$

How many hours would it take to apply a chromium plating of thickness $2.0 \times 1 0^{- 2}$ mm to car bumper of surface area 0.25m² in an electrolysis cell carrying a current of 75.0 A (Density of Cr = 5.25 gcm^-3)

(Round off to nearest integer)

TestHub · Accepted Answer

Volume to be covered = ( 0.25 × 1 0 4 cm 2 ) × 2 × 1 0 − 3 cm = 5 cm 3 Mass of Cr to be deposited = 5 cm 3 × 5.25 gm cm − 3 ​ = 52 5 × 5.25 ​ = 0.5 m o l ​ ​ C r 2 ​ O 7 2 − ​ + 14 H + + 12 e − → 2 C r + 7 H 2 ​ O For deposition of 2 mol Cr = 12 F electricity required For 0.5 mol Cr = 2 12 ​ × 0.5 F Now, 96500 75 × t ​ = 2 12 ​ × 0.5 t ≈ 1 hr

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