00:01
To calculate the hydrogen ion concentration from a solution made from 35 milliliters of 0 .66 molar c6h5nh2 and 40 milliliters of hcl, we recognize that when hcl is added, represented as hydronium ion, it's going to react with the base, which i'll represent as b, and make its conjugate acid and water.
00:29
As long as we don't add more hcl than we have of the weak base, then we will have created a buffer solution where we have both the weak base and its conjugate acid.
00:42
So we can calculate the ph of the buffer solution using the henderson -hasselbalch equation.
00:50
Ph equals pka, which will be the negative log of the ka value, which they didn't give us, but they did give us the kb value for the base.
01:05
So if we take kw, 1 .0 times 10 to the negative 14, and divide it by kb, 4 .6, times 10 to the negative 7, this will give us ka.
01:19
We take the negative log of that to get pka.
01:23
Then the rest of the henderson -hasselbalch equation is plus the log of the molarity of the base, divided by the molarity of the acid, or it's easier and equivalent to just use a ratio of moles...