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.
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.
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
Isn’t water itself the pretty literal definition of 0 and it doesn’t become one or the other until it’s a solution with something else?
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.
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.
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
But is it +0 or -0? Neutral 0 is a lie, a measurement precision error.