Consider an electrochemical cell based on the reaction: 2H+(aq) + Sn(s) = Sn2+(aq) + H2(g). Which of the following actions would NOT change the measured cell potential?


lowering the pH in the cathode compartment

addition of more tin metal to the anode compartment

any of the changes listed here will change the measured cell potential.

increasing the pressure of hydrogen gas in the cathode compartment.

increasing the [Sn2+] in the anode compartment

Choice 2

The action that would NOT change the measured cell potential is:

"increasing the pressure of hydrogen gas in the cathode compartment."

This is because the concentration of hydrogen gas does not affect the equilibrium constant or the Nernst equation for this electrochemical cell. The other actions listed will cause changes in the concentrations of the reactants and products, which will affect the measured cell potential.

To determine which of the actions would not change the measured cell potential, we need to understand the factors that affect cell potential in an electrochemical cell.

The cell potential is calculated using the Nernst equation, which is given by:

Ecell = E°cell - (RT/nF) * ln(Q)

where Ecell is the cell potential, E°cell is the standard cell potential, R is the gas constant, T is the temperature in Kelvin, n is the number of moles of electrons transferred in the balanced equation, F is the Faraday constant, and Q is the reaction quotient.

Now, let's analyze each of the actions mentioned and see if they would affect the measured cell potential:

1. Lowering the pH in the cathode compartment:
Lowering the pH in the cathode compartment will increase the concentration of H+ ions (higher [H+]). According to the Nernst equation, since the concentration of H+ ions appears in the reaction quotient (Q), changing its concentration will affect the measured cell potential. Therefore, this action will change the measured cell potential.

2. Addition of more tin metal to the anode compartment:
Adding more tin metal to the anode compartment will increase the concentration of Sn(s) (solid tin). However, solid species are not included in the reaction quotient (Q). Therefore, changing the concentration of the solid metal will not affect the measured cell potential. Thus, this action will not change the measured cell potential.

3. Any of the changes listed here will change the measured cell potential:
This option states that all the listed changes will affect the measured cell potential. While options 1 and 5 do affect the potential, as discussed above, option 2 does not. Therefore, this choice is not correct.

4. Increasing the pressure of hydrogen gas in the cathode compartment:
Increasing the pressure of hydrogen gas does not affect the concentration of H+ ions or the concentration of Sn2+. Since these are the only species involved in the Nernst equation for this reaction, changing the pressure of hydrogen gas will not affect the measured cell potential. Therefore, this action will not change the measured cell potential.

5. Increasing the [Sn2+] in the anode compartment:
Increasing the concentration of Sn2+ ions will change the reaction quotient (Q) in the Nernst equation, which will affect the measured cell potential. Therefore, this action will change the measured cell potential.

In summary, the action that would NOT change the measured cell potential is the addition of more tin metal to the anode compartment.

What do you think and why? Hint: Which will NOT change the concn of the substance in any way?