 So let's try this one. It says, calculate the pH at the equivalence point for the following titration. 0.10 molar formic acid versus 0.10 molar sodium hydroxide. So, I've written all the pertinent information up here. We've got the k-h from the k-h table, okay? So, the first thing you're going to want to know is it's talking about the equivalence point, okay? But it doesn't give you any volumes. So you can assume that these are in one liter, okay? Or we've titrated one liter. So if we've got one liter solution of this, we've got one liter solution of this, then we'll have 0.10 moles of this, 0.10 moles of this, okay? So when we do that, we can set up the reaction equation, formic acid plus sodium hydroxide. So, the strong base reacting with the weak acid is going to go all the way. So, again, remember we said, if you want to write it out, so if we have one liter of each of these solutions, we can figure out the number of moles. It's going to be 0.10 moles of that and 0.10 moles. So, we can actually set an ice cable here, so we started with this, started with this, like that. So that's going to be 0 here. It's completely reactant. So we're going to have 0 there. It's completely reactant. So we can't do Henderson-Hasselbach on this one, okay? So in order to figure out what's going on, we're going to have to write another reaction equation, which is going to be, because we have this, the sodium formate. So H-C-O-O. And I'm just going to write it as the conjugate base. Because remember that sodium is a spectator on it, okay? So it's not going to participate in the reaction. So it's going to react with water, like that. Remember, this is a weak acid, weak base reaction, so it's going to be an equilibrium. So that's going to give us warmic acid plus the hydroxide. So we're going to do another ice cable here, okay? So what are we going to start out with? 0.10. Boulder, if you want, okay? Change is going to be minus x, 0.10 minus x. So we started with 0, started with 0, plus x, plus x. So we got x and x, like that, okay? So now let's go ahead and erase this top ice cable so we can have more room. So, mind is that we're going to need to figure out, well, what expression is this all equal to? Well, this is a weak base, so it's going to be the KB expression. KB equals the concentration of formic acid times the concentration of the hydroxide ion, like that. Provided by the concentration of the formic anion, like that. So KB, but we have KA here. Remember, the equation, KW equals KA times KB, okay? So what is KB? That's going to be KW divided by KA, like that. So this is 1.0 times 10 to the negative 14th, divided by 1.7 times 10 to the negative 4th, okay? So let's do that together. So I get 5.88 times 10 to the negative 11 for the KB of forming the formic anion. So, remember, that's a very small number. So we can do the 5% rule, like that. Okay, so let's now look at what we got. We got X and X, so let's plug in. This is going to be X, this is going to be X, right? X and X, there. Okay, so we're going to have KB, let's just put it in values for this since we're running out of time. So 5.88 times 10 to the negative 11 equals X times X, divided by 0.10, like that, okay? So, remember, X is the concentration of hydroxide ion, so if we rearrange this thing, we're going to have hydroxide ion squared equals 0.10 times 5.88 times 10 to the negative 11, okay? So that's 5.88 times 10 to the negative. So what's the concentration of the hydroxide ion? Well, it's going to be the square root of 5.88 times 10 to the negative 12. 2.43 times 10 to the negative 6 molar OH minus, okay? But we're looking for pH, right? So we don't need OH minus, right? We need H3O plus, right? So how do I do that? Remember, KW also equals concentration of H3O plus times the concentration of OH minus, right? So we can figure out what H3O plus is by saying KW divided by concentration of OH minus, which is going to be 1.0 times 10 to the negative 14 divided by 2.43 times 10 to the negative 6. How do that? I get 4.12 times 10 to the negative 9 molar H3O plus, like that, okay? So pH, here I'll just do it up here, pH, remember, is the negative log of the H3O plus concentration, right? So the negative log of what is it? 4.12 times 10 to the negative 9. That's going to be the log of that answer is 8.38. So that's carrying all your digits the whole time, okay? So that's the pH of this solution. Are there any questions on that one? Wonderful. Can I kill it? Yeah.