 Okay, so let's do the third part of this finding the pH during a weak acid strong base titration So now we're going to calculate the pH of the solution following Addition of 40 point zero zero mils of any oh, so Remember on these ones we going to do two different ice tables. Okay, the first ice table showing what happened when we Took The NaOH and added it to our acid here. Okay, so if you recall the number We got this from the last problem the number of moles of Propionic acid was zero point zero zero four zero zero zero moles Right, and we took that and that Okay, so this time we're going to have the number of moles of NaOH To be So if you can't do that in your head go ahead and calculate it out just like we did the last one So the first ice table CH3 CH2 CH2 Plus sodium hydroxide, but for sodium hydroxide we're just going to put the OH minus and that goes forward. Okay, so Here we're going to make Plus So what do we get here? Here Here Here, what are we going to subtract? This thing here right a whole thing. Okay, so Notice when we do that what happens we got zero there Okay, and also we're subtracting that right so we got zero there But what are we doing here? adding So our solution is no longer starting out with that acid. It's starting out with its conjugate base Okay, does that make sense? wonderful So I'm going to read I'm going to erase this and rewrite a new equation starting with the conjugate base. Okay using the ice okay, so I don't need any of this The form this number here is falling to come up here. What is it for? Kb, okay, so we're going to have to figure out what Kb is right. This is the base here Okay, so we got k a here right remember k w Equals k a times kb, so kb equals k w over k a 7.7 So that is very small everybody else aware of that so we can do this right Okay, so can I erase the ice table except for our equilibrium concentrations? So x and x right, so that's going to be x squared right so the concentration of OH minus going to equal the square root of Kb Times the concentration of the acid. Okay, I'm going to erase this So this is the number of moles of base we have but not the concentration right Okay, so that's the number of moles. How many mils do we have 40 plus 40? so It's going to be divided by 0.08 zero zero years like that So that's going to be the concentration of OH minus like that so Are now fully Profile Zero zero zero Hydroxide So kb here 7.7 times 10 to the negative 10 times zero point zero five zero zero zero square root I get 6.2 times 10 to the negative 6 molar OH minus so each three oh plus equals Kw divided by OH minus 2 times 10 to the negative 6 So 6 times 10 to the negative 9 polar So the pH the negative log of the hydronium ion concentration equals the negative log of 1.6 times 10 to the negative 9 Which equals are there any questions on that one? That I apologize for questions