Asked by corey

Find the grams of NaF added to 300ml of .2M HF to create a buffer with pH=3.5.

Answered by DrBob222
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]

Answered by corey
what is the Ka of HF?
Answered by DrBob222
I have a quant book that lists it as Ka = 7.2 x 10^-4
Answered by corey
I came up with -5.4 x 10^-4.
Answered by DrBob222
What's with the negative sign? Is that a value for Ka you found different from mine. The negative value makes no sense. Or is that the grams NaF to add? Again, the negative sign makes no sense.
Answered by DrBob222
I don't know what happened to my response to your post but I made it last night. It showed up on the boards but today it doesn't show UNLESS you click on the main link (the first link) to the question, then all the answers show. At any rate, click on that to get the response. Bascially, I don't understand the negative sign.
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