Hello- I can\'t figure out a homework problem. Ihave reread the problem and the

Question

Hello- I can't figure out a homework problem. Ihave reread the problem and the book and I still cant figure outhow to set it up. The problem reads: What is the pH of a buffer solution that is 0.40M sodiumacetate and 0.20M acetic acid. Book: Principles of General Chemistry, Selberg Hello- I can't figure out a homework problem. Ihave reread the problem and the book and I still cant figure outhow to set it up. The problem reads: What is the pH of a buffer solution that is 0.40M sodiumacetate and 0.20M acetic acid. Book: Principles of General Chemistry, Selberg

Explanation / Answer

We know that pH = pKa + log ( [salt] / [acid])                             = - log Ka +  log ( [salt] / [acid]) Given [acid] = 0.2 M          [salt] = 0.4M The dissociation constant for acetic acid , Ka = 1.8 *10^-5 Plug the values we have pH = - log Ka +  log ([salt] / [acid])                                           = - log 1.8 * 10^-5 + log (0.4 / 0.2 )                                           = 5 - log 1.8 + log 2                                           = 5 -0.2552 + 0.3010                                           = 5.0458                                           ~ 5.05

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