A student must make a buffer solution with a ph of 5.5. determine which of the acids and conjugate bases listed below are the best options to make a buffer at the specified ph.

Weak acid

Explanation:

The key to this question is understanding what we mean by

pH and pKa, which are logarithmic functions. Students tend to have problems with the logarithmic function. I will introduce the subject briefly.

When I write logab =c, I am asking to what power I raise the base a, to get b. Here ac = b. Now, usually we use the bases 10 or e. So log10100 = 2, log101000 = 3, log101000000 = 6. Likewise log100.1 = log1010 − 1 = −1. In the days before electronic calculators (approx. 30-40 years), students would be issued log tables so that complicated calculations could be performed.

From the above

pH = −log10[H3O +], and pKa = −log10Ka. These are simple functions that have been widely used in chemistry.

Now it is fact, that when a weak acid is mixed with its conjugate base in appreciable concentrations, a buffer solution is formed that tends to resist gross changes in

pH.

We can write, pH = pKa + log10 {[A−][HA]}.

It is clear that when [HA] = [A−], then pH = pKa because log10 {[A−][HA]} = log101 = 0

So we want an acid whose pKa ≅ pH . To get pKa

I simply perform the function

−log10Ka, on each of the acid dissociation constants.

pKaHA = 2.57; pKaHB = 5.36; pKaHC = 8.58;

We want to maintain pH at 5.5, so it is clear that acid HB

is the acid of choice

The best acids and conjugate bases to make a buffer solution with a ph of 5.5 are:

Explanation:

The under-listed steps are under taken to prepare a buffer solution with a pH of 5?

answer; talc and gypsum;