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Why is the pH of pure water i.e. neutral 7?


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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

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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)

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