00:01
To calculate the initial ph of the solution, we'll use the henderson -hasselbalch equation.
00:06
Ph is going to be equal to pka, which will be the negative log of the ka value for hypochlorous acid, which they didn't give to us, so we'll have to look it up in the table i have.
00:20
Hypochlorous acid has a ka value of 3 .0 times 10 to the negative 8.
00:28
We then add to that the log of the concentration of the base, which will be the hypochlorite.
00:38
So a 100 ml buffer solution contains 0 .150 molar hypochlorite and 0 .175 molar hypochlorous acid, and we get a ph of 7 .455 or 7 .46.
01:04
Then when we add the hbr to it, the hbr, which i'll represent as hydronium ion, is going to react with the base that's present, the hypochlorite, and produce the hypochlorous acid and water.
01:28
So we can calculate the ph in a similar fashion.
01:31
Ph will be equal to pka, the negative log of 3 .0 times 10 to the negative 8, plus the log of, instead of using the molarity of the base over the molarity of the acid, we can use mole's base over mole's acid.
01:49
That's going to be easier and equivalent in this case.
01:54
So the moles of base will be the moles we started with, 100 ml, which is 0 .100 liters, but a concentration of 0 .150 moles per liter.
02:08
And then every mole of hbr we add consumes a mole of the base hypochlorite, so we'll subtract off the moles of hbr, which will be the mass of hbr, 150 milligrams is 0 .150 grams, converted to moles using the molar mass of hbr.
02:33
The molar mass of hbr will be the mass of one mole hydrogen and one mole bromine, giving us one mole is 80 .912 grams.
02:49
So this is the moles of hbr we add, but it's also the moles of clo minus consumed...