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If the pH is 2.5 what is [H3O+] and [OH-] and if pOH is 4.6 what is [H3O+] and [OH-]    

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mpumpkin | Salutatorian

Posted May 20, 2013 at 2:28 AM via web

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If the pH is 2.5 what is [H3O+] and [OH-] and if pOH is 4.6 what is [H3O+] and [OH-]

 

 

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted May 20, 2013 at 2:43 AM (Answer #1)

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The pH of a solution is defined as `-log[H3O+] = log(1/[[H3O+]])` . The pOH of a solution is defined as `-log[OH-] = log(1/[[OH-]])` . For any solution the sum of pH and pOH is equal to 14.

For a solution with pH 2.5, `log(1/[[H3O+]]) = 2.5`

=> `1/([H3O+]) = 10^2.5`

=> `[H3O+] = 10^-2.5`

`[OH-] = 10^-(14 - 2.5) = 10^-11.5`

Similarly if the pOH is given as 4.6, `log(1/([OH-])) = 4.6`

=> `1/([OH-]) = 10^4.6`

=> `[OH-] = 10^-4.6`

`[H3O+] = 10^-9.4`

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