Question

The following questions refer to the following acids and bases.
A) Hydrazoic acid HN3 Ka = 1.9 x 10^-5
B) Hydrofluoric acid HF Ka = 6.8 x 10 ^-4
C) Nitrous Acid HNO2 Ka = 4.5 x 10^-4
D) Phenol C6H5OH Ka = 1.3 x 10^-10
E) Aniline C6H5NH2 Ka = 4.3 x 10^-10

1) which compound is best when preparing a buffer of pH = 9.5?

2) which .20M solution will have the lowest pH?

3) Which .10M solution will have the lowest percentage ionization?

4) rank the compounds in order of increasing acid strength, lowest to highest.
A) D<E<A<C<B
B) E<D<A<C<B
C) D< E< A< B< C
D) B< C< A< E< D
E) None of these

If you include explanations that be great!

Answer 1

Zach, this is about a 20 question post which I've done several times in the last day or so. All of these questions are similar. Can you summarize what it is you don't understand about these. We need to get at the root so you can do these yourself.

Answer 2

How exactly do you get pH from Ka?

Answer 3

You don't get pH from Ka UNLESS you have the concentration of the acid. In this case you don't have that so you can't get a straight pH. If you are referring to the first question, which is
<b>The following questions refer to the following acids and bases.
A) Hydrazoic acid HN3 Ka = 1.9 x 10^-5
B) Hydrofluoric acid HF Ka = 6.8 x 10 ^-4
C) Nitrous Acid HNO2 Ka = 4.5 x 10^-4
D) Phenol C6H5OH Ka = 1.3 x 10^-10
E) Aniline C6H5NH2 Ka = 4.3 x 10^-10

1) which compound is best when preparing a buffer of pH = 9.5?
</b>
You answer that by remembering that the Henderson-Hasselbalch equation is
pH = pKa + log (base/acid)
When preparing a buffer you want the pH of the desired buffer to be close to pKa. That's because when (base)/(acid) = 1, then log 1 = 0 and pH = pKa.
You get pKa by pKa = -log Ka. So you find the pKa of each of the acids and pick the one closest to the pH of the buffer you want to prepare.