Homework Help: chemistry

Posted by flame on Thursday, November 11, 2010 at 4:03pm.

if 0.4M NaOH is titrated with 0.4M HF, how do we calcualte the ph at equivalence. The book assumes each is 1L, but why do we use 1L

* chemistry - Dr.Jim, Thursday, November 11, 2010 at 5:31am

HF is a weak acid, so you need the dissociation constant. The pH at the equivalence point is found by calculating the pH of a 0.4M NaF solution (a hydrolysis problem). If you erroneously assume that HF is a strong acid, then the answer is simple. The pH at the equivalence point is 7.

how can a weak acid and strong base titration has ph=7 at equivalence. It's only when they are both strong acid and base

chemistry - DrBob222, Thursday, November 11, 2010 at 4:47pm
I had trouble knowing where your question ended and Dr Jim's response ended. I think you asked one question not answered previously; why 1 L was chosen?

Why 1L? It's a convenient number to chose. You could have chosen any other number and the pH would be the same.

If you asked another question buried in there somewhere, please post again at the top of the page and someone will pick it up.

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