Comment on Is water an acid or a base?

• CookieOfFortune@lemmy.world ⁨1⁩ ⁨week⁩ ago

  Also I’m pretty sure it’s only coincidentally 7. The calculation for pH isn’t based any property of water.

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  • wolframhydroxide@sh.itjust.works ⁨1⁩ ⁨week⁩ ago

    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 at 298K, IIRC. So perturbations naturally just displace that specific equilibrium, so it absolutely is normative to water.

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    • NielsBohron@lemmy.world ⁨1⁩ ⁨week⁩ ago

      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

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    • CookieOfFortune@lemmy.world ⁨1⁩ ⁨week⁩ ago

      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?

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      • WalrusDragonOnABike@reddthat.com ⁨1⁩ ⁨week⁩ ago

        The exact value varies with temperature, so it’s a “good enough for the typical variations in temperature experienced by most aqueous solutions” estimate.

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• 21Cabbage@lemmynsfw.com ⁨1⁩ ⁨week⁩ ago

  Right, whatever the midpoint was. It’s been a minute since my last chemistry class.

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