00:01
Okay, so this question consists of two parts.
00:06
Part a is asking us to calculate the ph of a buffer solution of formic acid.
00:15
So the way we can do that is we can use the general equation for a buffer solution, which i have written here, is the hydrogen ion concentration or the hydronium ion concentration.
00:31
I believe the book has it written as hydronium, but essentially this is the same thing.
00:39
Equals the ratio of the concentration of the acid to its conjugate base times the equilibrium constant of the acid.
00:50
So the acid we are dealing with in this problem is formic acid.
00:55
So i have the equilibrium constant written here.
01:01
And so we can start plugging the values that we're given in the problem into this equation.
01:09
So our hydrogen ion concentration is going to equal the concentration of formic acid, which is 0 .050 molar, 0 .050 molar, divided by the concentration of the concentration, of the conjugate base, which in this case is given by sodium formate, which is a salt of sodium and the formate ion.
01:52
So that is going to be .035 is what we're given in the .035 molar.
02:09
And we can multiply this by the k .a.
02:16
Of formic acid, and that is going to give us a hydrogen ion concentration.
02:31
So we'll do h plus that is equal to 2 .57 times 10 to the negative fourth.
02:58
And to get ph, what we do is we take the negative log of this.
03:05
So if we take the negative log of both sides and the negative log of, i'll just write it like this.
03:20
So this is just saying we're taking the negative log of both sides of it.
03:24
So ph is going to equal 3 .5.
03:41
And so that is the answer to part a.
03:44
So what part b asks us is what the ratio of acid to conjugate base needs to be if we increase the ph by 0 .5.
03:57
So i'm going to erase some of this to make some space.
04:03
So i'm going to erase the calculation we just did.
04:10
And so our new ph, since we want to increase it by 0.
04:17
5 is going to be 4 .09.
04:30
And so 4 .09 is our ph...