Nickel is a transition element and has a variable valence. Using a nickel salt,

Question

Nickel is a transition element and has a variable valence. Using a nickel salt, 2.00 faradays plate out 39.2 g of nickel. What form of nickel ion is in the solution of this salt? (A) Ni^+ (B) Ni^2+ (C) Ni^3+ (D) Ni^4+ The standard cell potential, E degree for this reaction is 0.79 V. 6I^-(aq) + Cr_2O_7^2-(aq) + 14H^+(aq) rightarrow 3I_2(aq) + 2Cr^3+(aq) + 7H_2O(l) What is the standard potential for I_2(aq) being reduced to I^-(aq) given that the standard reduction potential for Cr_2O_7^2-(aq) changing to Cr^3+(aq) is +1.33 v? (A) +0.54 V (B) -0.54 V (C) +0.18 V (D)-0.18 V

Explanation / Answer

5) One F of electricity deposits equivalent weight amount of substance

i.e.-  One F of electricity deposits equivalent weight(EW) amount of Ni

or, Two F of electricity deposits 2x EW amount of Ni

Given that, amount deposited = 39.2 gm

Thus, 2x EW of Ni =  39.2 gm

or, EW of Ni = 39.2 / 2 = 19.6 gm

atomic mass of Ni = 58.7 gm/mole

EW = (atomic mass) / valency

or, Valency = (atomic mass) / EW = 2.99 (nearly equal to 3)

Thus, Ni is present in the form of Ni3+ in the salt.

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