Well, yes and no. The pH scale follows the hydrogen ion concentration, but specifically in aqueous media. The reason 7 is in the “middle” of the scale is because the natural dissociation of water sits at equilibrium at 10^-7 M H+ at 298K, IIRC. So perturbations naturally just displace that specific equilibrium, so it absolutely is normative to water.
Interestingly enough, in other solvents a neutral pH is going to be a different value. IIRC, ammonia has an autoionization constant of 10^-30, so a neutral pH would be 15
By that definition, it can’t be exactly 7 then either. 10^-7 is just an estimate that we’ve agreed works fine. To my knowledge we haven’t really tried to improve this accuracy either?
The exact value varies with temperature, so it’s a “good enough for the typical variations in temperature experienced by most aqueous solutions” estimate.
Water is the definition of 7.
Right, whatever the midpoint was. It’s been a minute since my last chemistry class.
Also I’m pretty sure it’s only coincidentally 7. The calculation for pH isn’t based on any property of water.
Well, yes and no. The pH scale follows the hydrogen ion concentration, but specifically in aqueous media. The reason 7 is in the “middle” of the scale is because the natural dissociation of water sits at equilibrium at 10^-7 M H+ at 298K, IIRC. So perturbations naturally just displace that specific equilibrium, so it absolutely is normative to water.
Interestingly enough, in other solvents a neutral pH is going to be a different value. IIRC, ammonia has an autoionization constant of 10^-30, so a neutral pH would be 15
By that definition, it can’t be exactly 7 then either. 10^-7 is just an estimate that we’ve agreed works fine. To my knowledge we haven’t really tried to improve this accuracy either?
The exact value varies with temperature, so it’s a “good enough for the typical variations in temperature experienced by most aqueous solutions” estimate.