So I was thinking about pH today and realized why water was so important in defining the scale. It isn't just that water neutral between different Bronsted-Lowry Acids. pH is defined by water.
Water is the simplest molecule with both H and OH and acts as the solvent for most mixtures. We know that pH varies from 0 to 14. That means that water can, at most, accommodate 1 Mol of Hydrogen atoms (pH 0). It has a maximum hydrogen carrying capacity (H3O+ max -- this is most acidic). Measuring a pH gives a sense of how much the solute is stressing or alleviating water hydrogen carrying capacity.
Conversely, in a basic solution there must be at least least .00000000000001 M (13 zeros) of water -- for if there were fewer, there would be an enormous stress in the solution to create more. You can make them from all the excess OH floating around.
So pH is a way to thing about how much stress is being put on the water to hold extra hydrogen atoms. But you can imagine that these carrying capacities vary between solvents. That the same solute will have different pHs in different solvents. Ethanol has its own hydrogen carrying capacity which will influence the solute's acidity or alkalinity. In fact, something that's acidic in water can be basic in ethanol.
An interesting and clear explanation of all these ideas are here.
It makes sense then how acid and base equilibrium constants are defined. Acid equilibrium constant is concerned with the acid's capacity to add H to water (you see the solute on right with water and its products are the acidified water and conjugate base). The opposite is true for the base equilibrium constant (you see the basic solute and water on the reactant side and on the product side you see the conjugate acid and what's left of the water molecule).
Water is the simplest molecule with both H and OH and acts as the solvent for most mixtures. We know that pH varies from 0 to 14. That means that water can, at most, accommodate 1 Mol of Hydrogen atoms (pH 0). It has a maximum hydrogen carrying capacity (H3O+ max -- this is most acidic). Measuring a pH gives a sense of how much the solute is stressing or alleviating water hydrogen carrying capacity.
Conversely, in a basic solution there must be at least least .00000000000001 M (13 zeros) of water -- for if there were fewer, there would be an enormous stress in the solution to create more. You can make them from all the excess OH floating around.
So pH is a way to thing about how much stress is being put on the water to hold extra hydrogen atoms. But you can imagine that these carrying capacities vary between solvents. That the same solute will have different pHs in different solvents. Ethanol has its own hydrogen carrying capacity which will influence the solute's acidity or alkalinity. In fact, something that's acidic in water can be basic in ethanol.
An interesting and clear explanation of all these ideas are here.
It makes sense then how acid and base equilibrium constants are defined. Acid equilibrium constant is concerned with the acid's capacity to add H to water (you see the solute on right with water and its products are the acidified water and conjugate base). The opposite is true for the base equilibrium constant (you see the basic solute and water on the reactant side and on the product side you see the conjugate acid and what's left of the water molecule).
