The Reaction Quotient & Ksp

Jules Bruno
Was this helpful?
Hey, guys. So here, in this example question it says Willett precipitate form when 0.1 leaders off 500.100 Moeller lead two acetate and 20. leaders off 0.20 Moeller Potassium chloride are mixed here. They tell us that the K s P value of lead two chloride is given as 1. times 10 to the negative five. Now, since they're giving us K sp for this ionic compound, that's the compound we're gonna be dealing with. So P B C l two k s p is for ionic solids. So too solid We show how it breaks up into ions. So breaks up in tow led to ion plus two chloride islands. So we're gonna say ice chart, initial change equilibrium. Now we're gonna need room to work out the rest of this question, guys. So let me take myself out of the image. Realize here that this is not being thrown into pure water, so we're gonna have initial amounts. This is a solid first, though, so he ignored. Realize you have the word off means multiply. Remember that moles equals leaders Time similarity Realize here that this compound has in it lead two ions just like we have led to eye on here. And this compound here has chloride ions, just like we have chloride ion here. So when we work this out, we're gonna get initial concentration for both of our ions, this ion and this ion. So this represents a double common ion effect, and we're going to say that any time we're dealing with a double common I in effect, this basically is telling us that we're dealing with a Q versus K SP Question This will help us determine will precipitate form or not. So again, anytime they give us initial amount for both reactions or they're talking about precipitate in K S P, then there really hinting at us doing a Q versus K SP question. All right, so let's work this out. So we have 0.150 leaders off, Remember, off means multiply so are multiplying here. So when I multiply this out, it gives me 0.150 moles off lead to a city. But we just want lead to not lead two acetate sold to one more conversion for every one mole of lead two acetate. We're going to say we have exactly one mole of lead to because there's only one light in there. So this is 0.150 moles I'm glad to. But remember, with a nice chart, what units do we use? We use more clarity. So we even among clarity now of lead to asset of lead Thio Ion Remember, morality is moles over leaders. We found the moles. Now we have two divided by the total leaders. How do we figure out our total leaders? Well, that's just 0.150 leaders plus 0.100 leaders. So that's a total volume off 0.250 leaders. So that comes out 2.6 Mohler of lead two ions. Now we do the same thing for chloride ions. So we go back up here. So we have here 0.100 leaders times 0.20 Moeller off potassium chloride. So that comes out 2.2 moles of potassium chloride and we change that chloride ion. So for every one bowl of the whole compound, we have exactly one mole off chloride ion. Okay, so this equals 0.2 moles off fluoride ion divided by the total volume again will give us the polarity of chloride ions, which is 0.8 Mueller chloride ions. Their products are making them. So this is plus X. There's a two year So this is plus two x 0.6 plus X 0.8 plus two X. Now, since we have actual numbers, that means we can ignore the X variables. So we're gonna ignore these X variables. Now, these two initial amounts are not gonna help me to deal with K SP. What they're gonna help me figure out actually is cute and queues just like A S p equals products Overreactions. But our reacted is a solid. So we ignored so cute as equals P B two plus time seal minus again. Remember the coefficient forms of power to the second plug in the numbers that we have. So when we plug all this in, this gives us 3.84 times 10 to the negative four. So that's our cue. And remember, anytime we're dealing with Q and K sp, we do a number line. So K s P is equal a room where we wanna be. It is 1.2 times 10 to the negative five. We just found out what Q is que is bigger because to the negative fourth and we always ask ourselves when we look at Q and K. SP remember. Q is going to shift T K because we want to get to equilibrium. So which direction is CUNY to shift to get to K Que needs to shift to the left to get to K, and if it shifts to the left on the number line, it also shifts in the same exact direction in our equation. And remember, wherever we're heading is increasing. And if this side is increasing, this side here is decreasing. So the question originally asked, will precipitate form. Remember, a precipitate is a solid. So they're asking. Is the amount of solid increasing we'd say Yes, it iss We'd say Yes, a precipitate with form because we're shifting towards the solid. And why was shifting towards a solid? Because when we did the number line, we saw that Q was bigger than Ks P. So we have to move in the reverse direction to get back to equilibrium. As you can see, there's a lot involved in answering this question. But these are the steps we have to do when we're trying to do. Q versus K. S. P.