ed84c Posted October 21, 2004 Share Posted October 21, 2004 Why is the pH of pure water i.e. neutral 7? Link to comment Share on other sites More sharing options...
Gilded Posted October 21, 2004 Share Posted October 21, 2004 Since it was thought it's cool to have a pH scale of 0 to 14, and pure water in the middle of it. Actually, I'm not 100% sure of the origin, it probably has a greater reason than the one I mentioned. Link to comment Share on other sites More sharing options...
wolfson Posted October 21, 2004 Share Posted October 21, 2004 In pure water, the hydrogen ion (hydroxonium ion) concentration must be equal to the hydroxide ion concentration. [OH-] term in the Kw expression by another [H+]. [H+]2 = 1.00 x 10-14 Taking the square root of each side gives: [H+] = 1.00 x 10-7 mol dm-3 Converting that into pH: pH = - log10 [H+] pH = 7 Link to comment Share on other sites More sharing options...
Gilded Posted October 21, 2004 Share Posted October 21, 2004 Ahh yes, the logarithm thing. I knew it had something to do with those, but since I'm going to have my first logarithm lessons (ever) in a week or so, I had no idea it goes that way. Link to comment Share on other sites More sharing options...
dryan Posted October 21, 2004 Share Posted October 21, 2004 Since it was thought it's cool to have a pH scale of 0 to 14, and pure water in the middle of it. Yeah, but 10M HCl has a pH of -1, and 10M BaOH has a pH of 15, so the scale from 0-14 only works for dilute acids and bases (less than 1M) Link to comment Share on other sites More sharing options...
Gilded Posted October 22, 2004 Share Posted October 22, 2004 Yeah, but the usual scale is 0-14. Of course, there are incredibly strong acids that don't even need to have H+ or OH-. Link to comment Share on other sites More sharing options...
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