00:01
To calculate the concentrations of benzoic acid and benzate in the buffer, we first need to calculate the ratio of the concentration of the base benzoyate to the acid -benzoic acid.
00:16
To do that, we'll use the henderson -hasselbalch equation, where ph 4 .10 equals p .k .a.
00:24
4 .20 plus the log of the concentration of the benzoyate, the base, or the concentration of the of the acid, benzoic acid.
00:35
And doing a little bit of algebra, the base to acid ratio is equal to 0 .794.
00:47
So that means the base concentration is equal to 0 .794 of the acid concentration.
00:56
And we know the acid concentration plus the base concentration equals 50 .0 millimolar, but the base concentration we can replace with 0 .794 the concentration of the acid.
01:20
This then allows us to calculate the concentration of the acid.
01:25
So we have 27 .9 millimolar benzoyal acid, and then the concentration of the base is equal to 0 .7.
01:40
9 for the concentration of the acid, 27 .9 millimolar.
01:50
So that gives us 22 .1 millimolar benzoyate.
02:02
So to calculate the ph after the addition of 0 .0 .221 moles of hcl, ph will still be equal to pca, 4 .20, plus the log of, if we have a liter of solution at 22 .1 millimolar.
02:25
That means we have 22 .1 millimoles of the benzoyate...