 Okay, so this one says the pH of a 0.30 molar solution of a weak base is 10.66. What is the Kb of the base? Okay, so this is the information that was provided to us, let's attempt to solve this problem. So the first thing you want to do is be able to write the reaction equation for this problem. So what we're going to be doing here, of course, is an ice table so we can set that up right now. We have the original concentration of the base, 0.30. It's a weak base, so Kb is going to be very small, so we're going to be able to do the 5% rule this time. So let's just calculate everything else, at least as far as the ice table is concerned. So we have 0.30 minus x, so we have 0 and 0 starting now, so it's going to be plus x, plus x, so x, and x like that. So, if you recall, Kb is going to be the equilibrium constant of this reaction here. So let's go ahead and actually write out the expression for Kb. So Kb equals the products raised to their coefficients, Hb plus, that's the concentration of OH minus, divided by the reactants raised to their coefficients, divided by B. So is everybody okay with what we've done so far? Yes. Wonderful. I like that. So, 5% rule says we can wipe out that minus x there. The other thing is we have a pH value here, okay? So that's going to kind of, remember if we look at this reaction equation, this is the only thing that's going on in our solution, right? Is everybody okay with that? It's the only reaction. So out of all of these things, the only thing that's going to contribute to the pH raising or lowering is this hydroxide ions right here. So we can actually figure out what x is straight away, okay? So that's how we're going to have to do this. So remember pH, pH equation, negative log of the hydronium ion concentration, like that. So the hydronium ion concentration is 10 to the negative 10.66 like that. I get 2.19 times 10 to the negative 11 mole, okay? So that's for the hydronium ion concentration. So remember the KW expression is the hydronium ion concentration times the hydroxide ion concentration, right? And that's what we're looking for. Does everybody understand that? We're looking for that hydroxide ion concentration. So we can, good morning. So we can reframe this equation to solve for hydroxide ion concentration, which will be effectively solving for x. So we can do that, KW divided by hydronium ion concentration, like that. Remember KW is a constant, 0.0 times 10 to the negative 14. That'll be given to you. You don't have to memorize it. So 1.0 times 10 to the negative 14 divided by 2.19 times 10 to the negative 14. Times 10 to the negative 11. I give us our hydroxide ion concentration. I get 4.57 times 10 to the negative 4th molar for the hydroxide ion concentration. Okay? So we can think about that being x, right? So that means that's the same number, right? Because x equals x, right? So if that equals x, then that must equal that, too. Okay? So is everybody okay with me just erasing those two x's and putting that concentration value in there for it? 4.57 times 10 to the negative 4. 5.7 times 10 to the negative 4. Like that. So let's go back to KB. So this is what we're solving for. Remember, this is x. This is x. And we've got that from our original concentration. 4.57 times 10 to the negative 4. Times 4.57 times 10 to the negative 4. If you wanted to just say squared, you could do that. Divided by 0.30. Like that. So I'm just going to write out what I just said. So 4.57 times 10 to the negative 4. Square divided by 0.30. It's going to give you a KB. Okay? So let's do that all together. So square that answer and divide it by 0.30. And this is going to be two sick things, right? So there's a missed number here. So what do I get? 7.0 times 10 to the negative 7. Is everybody okay with doing that type of a problem? Any questions on that one?