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

Video transcript

hi everyone for this problem. It reads using the figure below determine which indicator is appropriate for the thai tradition of hydrogen cyanide with a strong base. Okay, so for this problem where we want to identify which one is going to be the appropriate indicator and each indicator below has its own ph based off of the image given. So we know we're dealing with the tight rations and hydrogen cyanide. This is a weak acid and we know we're dealing with a strong base. Okay, so in order for us to solve this problem, we can assume the following. We can assume that we're at the equivalence point and what that means is at the equivalence point our moles of acid is equal to are moles of base. Okay, so at the equivalence point this is true. So we're going to assume that the concentration of acid is the same as the concentration of base. So that means the total volume of our solution will have doubled. Okay, so if we assume that this is 0. molar, then that means our concentration of conjugate base is going to equal about 0.5 molar. So, this is an assumption that we can use to solve this problem. And the equation that we're going to use to solve this problem is the the equation is going to be the based association constant equation. Okay, which is our KB is equal to K W over K A. So the K W is the auto ionization of water, which has its own value over K A. Which is our acid dissociation constant. Okay, so because we're dealing with a conjugated base here, this is going to equal the concentration of hydroxide ions squared Over 0.05. Okay, so this should be 0.05 molar here. Okay. And so with that we can go ahead and isolate our hydroxide concentration because this is what's going to give us P. H. So we want to factor this out and solve for it. So we can go ahead and write out that the concentration of hydroxide ions is equal to the square root of 0.05 times K. W. Over K. A. Okay. And we already know what the value of K. W. Is. So we can just go ahead and plug in here. So we have 0.05 times 1.00 Times 10 to the - over A. K. A. So if we simplify this even more we get five times 10 to the negative 16 over K. So this is what it's going to give us our equation for P. H. Because our hydroxide ion concentration is going to be P. H. Is equal to plus log of what we just solved for. So five times 10 to the negative 16 over K. So this is what's going to give us our ph but we're missing our K. A. Which is our acid dissociation constant. This is a value we can look up And because it's needed, we're going to need to plug it into this equation. So the acid dissociation constant for hydrogen cyanide is 4.9 times 10 to the negative 10. So let's go ahead and now plug that in to the denominator. Okay, 4.9 times 10 to the -10. Alright, so we're going to get ph is equal to About 11. Okay, so now let's go up to our image and we'll draw a line where our ph is 11, and we're going to try to find the indicator that most closely reaches this ph. Okay, so out of all of the answers were given four answer choices. So let's just highlight them so we can visually see. Okay, so we have this one is A. This is B. This is C. And this is D. So out of these, which ph is most closely to 11. We can see that the answer is going to be answer choice A. Okay, so we can go ahead and erase this. So the correct answer for this problem is going to be a. This is going to be the indicator that is most appropriate for the titillation of this weak acid with a strong base. That's it for this problem. I hope this was helpful