[shafaifer]

5(a) Estimate the redox potential of water that is in equilibrium with the atmosphere (21% oxygen)
at pH 7 and 298 K, given that the standard reduction potential for O2(g) + 4H⁺ + 4e^- 2H2O(l) is
1.23 V, so I calculated:

E_cell=E^o_cell-(RT/nF)ln(Q)=1.23 V - (8.314 J/(K mol) * 298 K / 4 mol * 964853365 C mol^-1) * ln(10^-yM) = 1.230010347 V

Do you think it is correct?

With good regards

[unsu]

My version - you start with

E = E°+(RT/nF)ln[a(O₂)×[a(H⁺)]⁴]

[shafaifer]

My version - you start with

E = E°+(RT/nF)ln[a(O₂)×[a(H⁺)]⁴]

Thank your

I was forgetting the power to the fourth - for that I am sorry.

How does one obtain the activity of O₂?

[unsu]

activity of the oxygen gas is its partial pressure,
if the atmospheric pressure is 1 atm, then p(O₂)=0.21 atm, and a(O₂)=p(O₂)/p₀=0.21

[Borek]

Beware: these days standard pressure is 1 bar, not 1 atm.

[mjc123]

And your value of the Faraday constant is 4 orders of magnitude out.