Option 1: No change to equilibrium will be observed as addition of liquids or solids will not affect equilibrium.
Option 2: The equilibrium will shift towards left because the addition of H2O means that more H+ ions will be present in the system due to auto ionization of water into H+ and OH− ions. In order to offset the increase of H+ ions, the equilibrium will move towards left (reactants, in present case HF (aq))
First, the answer. An addition of water will result in dilution of HF.
Second. Your both options indicate that you must learn basics of acid-base equilibria.
Dear Alastair, why you have recommended this question? I'm just curious.
Dear Yurii,
I recommended this question because I am trying to teach myself about carbonate chemistry in the oceans.
I am also unsure which of the two Options will occur for HF. I suspect it is Option 2 but the increase in [H+] will be so small that it can be ignored and Option 1 will be the effect.
I am also interested in a related problem, which is why are [H+] and [OH-] included in the calculation of Total Alkalinity. Alkalinity is the buffering effect against changes to pH. The amount of [H+] won't affect that will it?
Dear Alastair,
none of options is correct. I'll send you by e-mail my presentation on acid-base equilibria. Yurii
When pure water is added, the concentration of all members of the equilibrium will be diluted by the same amount, so the simple equilibrium is not changed in a first approximation, when concentrations are not too low. The usual approximations neglect water dissociation in these conditions. But at very low concentrations, water dissociation must be taken into account, because, as suggested, the H+ will come from the dissociation of both HF and H2O. May be this aspect is included in the Yurii presentation on acid-base equilibria.