Referring to Table 17.1, pick an indicator for use in the titration of each base with a strong acid. a. CH3NH2

Video transcript

Hi everyone for this problem. It reads using the figure below determine which indicator is appropriate for the tight rations of the following molecule with a strong acid. So for this problem we're dealing with a tight tray shin. Okay. And we're told we have a strong acid and this molecule here, this molecule is called Chavez scene and it is a weak base. Okay. So we have a weak base and a strong acid and a tin tray. Shen is a lab technique that's used to measure the molar concentration of an unknown. Using unknown solution. Okay, so for this problem specifically we want to determine which indicator okay, is going to be appropriate and because we have a weak base it's going to dissociate partially in solution to produce hydroxide ions and the conjugate base. So we can do a couple of things here. We can assume that we're at the equivalence point. And what that means is our equivalence point is where our moles of acid equals our molds of base. So if we assume that the concentration of the acid is, the concentration of the base will know that the total volume of the solution will have doubled, doubled. Okay, so we're going to assume we're out equivalence And so our concentration of acid is going to equal our concentration of base. So let's just assume we have 0.1 molar. Okay, so that means our conjugate base concentration is going to equal about half of that. So we'll have about 0.5 molar. So that is the assumption that we're going to use for this problem. So we're given four indicators and each has its own P. H. So we need to identify which one is going to be the correct or the most appropriate. Alright, so the equation that we can use is our acid dissociation constant and our acid dissociation constant is reflected by K. A. And this value is equal to K. W over K. B. And this is the same thing as our concentration of products over our concentration of reactant. So our products is going to be we're going to have the hydro ni um ions. Okay, we're going to have our conjugate base and we're going to have our strong acid. Ok, so essentially what this means is our acid dissociation constant is going to equal our hydro ni um ion concentration squared over R K B. Okay, our base equilibrium constant. So what we want to do here is we want to solve for our hydro ni um ion concentration because this is what's going to give us our P. H. Once we find that P. H. We can see which ph is going to be closest out of the options that were given in this problem. So let's go ahead and isolate this out so that we're solving for our hydro ni um ion concentration. Okay, so if we factor this out so we have our hydro ni um ion concentration, we're going to factor it out and then cross multiply. So it's going to equal the square root of 0.5 times KW over K B. We know what our K W value is. This is 1.0 times 10 to the negative 14. Okay, this is a value we should know. So we have 0.5 Or this should be 0.05. Okay, so let's go ahead and make that correction here. So about 0.05 molar. So under the square root it should say 0.05. Okay, so we have 0.5 times K W which is 1.0 times 10 to the negative four team over K B. Okay, so we'll go ahead and simplify this out a little bit. So we'll get the square root of five times 10 to the negative 16 over K b. So this is essentially P H is equal to that OK? Is equal to the square root of five times 10 to the negative 16 over K B. So in order for us to solve for the ph we're going to need the value for K B and once we find that value and plug in, we'll be able to see what the ph is. So our KB is our based association constant. And for Chavez seen, this is a value that we can look up. Okay, so let's look up that value. So the KB for Chavez scene. So we'll go ahead and write that. The KB is 1.6 times 10 to the negative six. Okay, so let's go ahead and plug that in. So we have the square root of five times 10 to the negative 16/1 100.6 times 10 to the negative six. Okay, So we can go ahead and plug in and when we do we get a P. H is equal to 4.75. So now that we know what our P. H. Is, we can find the indicator that is closest to this value out of the options given. Okay, so let's just draw a line on our image to see where is 4.75. Okay, so 4.75 is going to be about here. Okay, so let's see out of all the indicators given. Let's just highlight the indicators. Okay, so A is the this option here. Okay, B is here C is here and d is here. Okay. Out of these options, which indicator falls in that 4.75 ph range and we can see from our image is going to be our method red. So go ahead and highlight methyl red as our final answer. Okay. And that is going to be it for this problem. So the indicator that's appropriate for this tight rations is going to be answer choice C which is Methyl red. That's it for this problem. I hope this was helpful