Question

Consider the following reactions:

          3 Ni 2+(aq)  + 2Cr(OH)3 (s) + 10 OH –(aq)    →   3 Ni (s) + 2 CrO4 –2 (aq) + 8 H2O (l)

A) What is the value for n for this reactions?

B) Calculate the standard Gibbs Free-Energy

C) How long does it take a current of 5 A to deposit  95 g of nickel?

Answer 1

A) Value for n for this reaction is 6

B) $E^0_{cell}=E^0_{Ni^{2+}}/Ni+E^0_{Cr(OH)_3}/CrO_4^{2-}=-0.257v+0.130v=-0.127v$

$\Delta G^o =-nFE^o=-6\times 96485\times (-0.127)=7.352157\times 10^4J$

So, the standard free energy is $73.5kJ$

C) Equivalent weight of Ni=molar mass$/$ valency=58.6934$/2=29.3467g/Eq$

Amount of charge required to deposit 95g of nickel$=96485C/1Eq\times 1Eq/29.3467g\times 95g=312337.503C$

time required, $t=q/I=312337.503C/5A=62467.5006s$

convert into hours $62467.5006/3600=17.4hours$