 Kehlani F.

# Equilibrium constant value

A galvanic cell is based on the following half- reactions:

Cu+2 (aq) + 2e- à Cu (s)                  ɛ° = 0.34 V

V+2 (aq) + 2e- à V (s)                   ɛ° = -1.20 V

In this cell, the copper compartment contains a copper electrode and [Cu+2] = 1.00 M, and the vanadium compartment contains a vanadium electrode and V2+ at an unknown concentration. The compartment containing the vanadium (1.00 L of solution) was titrated with 0.0800 M H2EDTA2-, resulting in the reaction:

H2EDTA2- (aq) + V2+ (aq) ßà VEDTA2- (aq) + 2H+ (aq)     K=?

The potential of the cell was monitored to determine the stoichiometric point for the process, which occurred at a volume of 500.0 mL H2EDTA2- solution added. At the stoichiometric point, the cell potential was observed to be 1.98 V. The solution was buffered at a pH of 10.00.

a. Calculate the value of the equilibrium constant, K, for the titration reaction.

By: Tutor
4.9 (80)

Chemistry Tutor - High School, AP, College Ellen E.

I'm thinking, there are several opportunities to build your chemical intuitions in this problem. 1) Our calculation showed that the residual concentration of the V2+ is very small after titration. This makes sense, because that is how titrations are supposed to work. 2) Our calculated K is very large. This also makes sense because the V2+ remaining after titration is very small AND, again, this is what you expect for good titration reaction. Titrations are, as much as possible, based on reactions that "go to completion", which means they must have a very high K and very little reactants remaining after reaction. 3)Another intuition to build: The shift in E after the titration is QUITE LARGE. The standard potential is 1.54, and after the titration the E shifts to 1.98 is quite large. This makes sense if you look at the overall reaction for the Cell: V2+ is on the PRODUCTS side. Depleting the products, means the reaction must shift left, towards the products, to go back to equilibrium. The standard potential (calculated at 1M solution concentration) is much smaller than in the post-titration scenario, because the post-titration scenario has been shifted much further away from equilibrium. I hope this will help you tie together the concepts of equilibrium and electrochemistry.
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05/27/19

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