[victornumber]

I don't really have a clue how to do the following question. The only thing that I can tell is that since it is distilled water [H3O+][OH-]=kw and [H3O+]=[OH-].
Since the water is in equilibrium with air, the value of kw would be larger than 1.0X10^-14 due to more dissociation of water. In equilibium with air I think it means that the vapor pressure of water is the same as the atmospheric pressure. This is all I got. Does this have to also do with the gas law and the Clausius-Clapeyron Equation since it is partly dealing with gases and we know that the air pressure at 0C is 101.325kpa. Need hints please.

Find the pH of a sample of distilled water in equilibrium with air at temperature T (express your answer as a function of the relevant variables, don't make calculations).

[Borek]

What gases - other then O₂, N₂ and Ar - are present in the air?

[victornumber]

CO2, Ne, Helium, Kr, NO2, and Hydrogen and others but these I would say are not significant value since the three main components of air are N2, O2, and Ar but what has this have to do with the question?

[Borek]

Any acidic oxide between these?

[victornumber]

I would think CO2 and NO2. Do you mean that we also have to take these into account?

[Borek]

CO₂ only. pH of pure water saturated with atmospheric CO₂ is somewhere between 5.5 and 6.0 (5.6?).

[victornumber]

Thanks for the reply but the question we got we can only solve with variables and I can's seem to relate it. That is what is so hard.

Find the pH of a sample of distilled water in equilibrium with air at temperature T (express your answer as a function of the relevant variables, don't make calculations).

[Borek]

Relevant variables are IMHO - air composition, Henry constant, Ka values. Perhaps your prof was aiming at something else (no idea in what context this question was asked), but in practice CO₂ is the most important factor here.