Question

1) You need an acid that will spontaneously oxidize Sn, but NOT spontaneously oxidize Ag. How many of the following acids meet these criteria?:

Hydrochloride acid, iodic acid, nitric acid, periodic acid

a) 1

b) 2

c) 0

d) 3

e) 4

2) What is deltaG for the balanced disproportionate reaction of IO3- under standard conditions?

a) 386 kJ

b) 77.2 kJ

c) 193 kJ

d) -2.70 x 10^3 kJ

e) -193 kJ

3) What is the deltaG for the spontaneous reaction that will occur when Cr wire is dipped into an aqueous solution of CoCl2 under standard condition?

a) -88.8 kJ

b) -133 kJ

c)-266 kJ

d) -405 kJ

e) -608 kJ

f)-1.22 x 10^3 kJ

Answer 1

3) Half reactions:

Cr3+ + 3e- ---> Cr. Eº = -0.74V; Co2+ + 2e- ---> Co. Eº= -0.28V

Your first reaction has a DGº₁ and the second has a DGº₂. The overall reaction needs both half reactions, so that

2Cr + 3CoCl2 --> 2CrCl3 + 3Co, with DGº₃.

Then, DGº3 = 3DGº2 - 2DGº1... Consider that DG= -nFEº, in both cases

DGº3 = 3(2)(96485C)(-0.28V) - (-2)(3)(96485C)(-0.74V) = -266298.6 J.

The answer then is -266 kJ

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