A 250 mL sample of a 0.2 M C r 3 + is electrolysed with a current of 96.5 amp; if the remaining concentration of C r 3 + ion is 0.1 M, the duration of electrolysis is given : atomic mass of Cr = 52

Step-by-step solution

Number of moles of C r 3 + before electrolysis = M V ( mol ) 1000 = 0.2 × 250 1000 = 0.05 Number of moles of C r 3 + after electrolysed = M V 1000 = 0.1 × 250 1000 = 0.025 Number of moles of C r 3 + electrolysed = 0.05 - 0.025 = 0.025 Mass of chromium electrolysis = 0.025 × 52 = 1.3 g Equivalent mass of chromium = Atomic mass Valency of ions = 52 3 = 17.33 W = ItE 96500 ⇒ W × 96500 I × E = 1 . 3 × 96500 96 . 5 × 17 . 33 t = 75.14 sec ≈ 75 sec.