 So this will be the last problem we do today in office hours, so it says Which of the following solutions can act as buffer solutions? And then it gives you these four Okay, so What we're going to Remember about a buffer solution. You guys remember what a buffer solution is from the last lecture I know you all were studying for your exam I'm doing right here, but buffer solution is made up of a weak acid And it's a conjugate base, yeah Okay, so that gives you a clue as to what you need, right? You have to have a weak acid first Okay, and then the conjugate base of that weak acid So already I can cross off two of these, okay, so if I look up here, right? HCl that is not a weak acid. That's a strong acid. Okay, so can this be a buffer? No, it cannot be a buffer this one here Same reasoning sulfuric acid H2SO4 is a strong acid So we can't even though this is the conjugate base This is the conjugate base of that acid We look over here So we've got H2PO4 minus and HPO4 2 minus. That's a weak acid That's the conjugate base of a weak acid. So yes, that could be a buffer solution Okay, what is this one strong acid or weak acid? Do you guys remember how to identify? We cast it right is that its conjugate base? Do you remember how to do it? Cover that up and put a minus It's the conjugate base, okay, so can that be a buffer? Weak acid and it's conjugate base? Good job. Any questions on this one? So you got to know your weak acids and strong acids if you don't know that them And you got to know what your conjugate acid and conjugate bases are. You don't know that you can't do this