The pH Scale Example 2

Jules Bruno
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Hey, guys, In this new video, we're gonna continue with our calculations dealing with P H and P O H. So, in this question, it says a solution is prepared by dissolving 0. moles off strong team hydroxide in water to produce a solution with the volume of 750 amounts. Now I'm asking you to find the concentration of O H minus. Remember these brackets being concentration? Another name for concentration is molar ity. And remember, mole arat e equals moles of solute over leaders of solution. So here we need the moles of O H minus, divided by the leaders of solution. Let's do the easier part first. The easier part is we have 750 ml of solution. So let's just change that to leaders. So we're gonna say we have 750 m. Els. You can say here for everyone Leader, there's 1000 mL or you could say for everyone ml there's 10 to the negative three leaders, so that gives me 0.750 leaders that will go on the bottom. Now the harder part we have toe isolate moles off just hydroxide ion So all we're gonna do here is we're gonna take these 0. moles of strong team hydroxide and convert them into moles of hydroxide ion on Lee. So we're gonna say we have 0.235 moles off strong team hydroxide and then just simply say, here for every one mole of strontium hydroxide how maney hydroxide zahren the formula, you can notice that there are two of them, so there's two hydroxide for every one mole off strong team hydroxide. So that's gonna give me 0.4 70 moles. Oh, h minus. So we're gonna take those molds and plug them up top. So 470 divided by 4700.750 will give me 0.6 to 7 Moeller Oh, h minus. So that'll be your answer here. Now, for part being, I want us to find the H plus concentration. So remember, all we need to realize here is if I know my o h minus concentration, then I know my age plus concentration because, remember, they're connected by this formula. K w equals H positive times O h minus. Plug in what we know for K W. And then fill in what we know for O H minus. So we got to do now is divide both sides by 6 to and we'll know what h plus is. H plus comes out to be 1.59 times 10 to the negative. 14. Hope you guys were able to follow along this question just how to do with a little bit off, uh, unit conversions and some little bit of stoke geometric relationships. For every one mole of strong team hydroxide, we have two moles of O H minus. So now that we've seen that one, I want you guys to attempt to do this practice question here. So remember, go back and see what the relationships are in order to find this correct answer and just realized you when I say pure water, just understand pure water means neutral water. So if your water is pure, you're neutral water. And remember, what? What does that mean in terms of H plus and O H minus, knowing that will be the key to solving this question? Good luck, guys.