 Okay, so let's do this problem. So it says, a research chemist adds a measured amount of HCl gas to pure water at 25 degrees Celsius and it obtains a solution with the hydronium ion concentration as 3.0 times 10 to the negative fourth mole. Calculate the hydroxide concentration and then it wants us to say, is this solution acidic, basic, or neutral? Okay, hopefully you can look at this number here, the hydronium ion concentration, realize it's bigger than 10 to the negative seventh and say this solution is acidic, okay? But we're just going to eventually compare the hydronium to the hydroxide and without a doubt say that the hydronium is bigger, okay? So let's go ahead and do that. So in order to do this you have to remember the equation that relates hydronium to hydroxide. Like you guys remember that equation, what is it? Kw. Kw, very good. Times what? Concentration hydronium. Yeah, concentration hydronium ions, times what? Concentration hydroxide. Thank you. Okay, so in order to do this we have to rearrange this equation and you have to remember what Kw is, okay? So let's write Kw over here. 1.0 times 10 to the negative 14, okay, no use. So we want OH minus, so rearrange this equation. OH equals Kw divided by H3O plus, like that. Is everybody okay with doing something like that? Again, if we just calculate this out and plop our units there we get per molar, which is not the right units, okay? So watch out for that. We have to remember these are going to be a molar units, okay? So whenever you have those Ks they always mess up your units, okay? So 1.0 times 10 to the negative 14 divided by, I'm not even going to throw those units in there so we won't get no views, okay? Divided by H3O plus 3.0 times 10 to the negative 4. So you should be expecting this to be like, I don't know, around 10 to the negative 10th or something like that, right? So let's, let's get something, one second. Yeah, so we get 12 to 2 safe things, 3.3 times 10 to the negative 11. And we have to remember now to put molar in there. So that's a very, very small amount of hydroxide ions. So the hydroxide concentration is written there. So if you want to now really compare the hydroxides of the hydronium, hopefully you can see here that negative 4 as a super-script is much bigger than negative 11. Okay, and then from that analysis you can definitely say now we are an acidic solution. Is there any questions on this one? So again it's just that comparison, okay? And you need to have, have an understanding of the KW equation and remember KW is 1.0 times 10 to the negative 4. Okay, wonderful.