00:01
Remember, a buffer solution is most effective when the concentration of the acid equals the concentration of the conjugate base.
00:09
When this is true, according to the henderson -hasselbalch equation, that is ph equals pca plus the log of the base concentration over the acid concentration, then with this ratio being 1 and the log of 1 being 0, ph equals pka.
00:34
So the most effective buffer is going to be a buffer that contains a weak acid that has a pca as close to the ph that we desire.
00:45
So if we desire a ph of 5 .2, then we want to find an acid that has a pca close to 5 .2.
00:56
Hydro -iodic acid, it's pca, pca being equal to the negative log of the k.
01:05
Value so negative log of 1 .7 times 10 to the negative 1 is 0 .77 hydro iotic so that won't work.
01:27
The next one is boric acid and for boric acid if we take 5 .8 to the negative 10 and take its negative log p .a is equal to 9 .24 so that won't work.
01:47
If we have chloroacetic acid, we take the negative log of its value at 1 .4 times 10 to the negative 3.
02:00
And we get pca equal to 2 .85...