Which of the following solutions is a buffer? (a) A solution
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Question

Which of the following solutions is a buffer? (a) A solution 
made by mixing 100 mL of 0.100 M CH3COOH and 50 
mL of 0.100 M NaOH, (b) a solution made by mixing 100 
mL of 0.100 M CH3COOH and 500 mL of 0.100 M NaOH, 
(c) A solution made by mixing 100 mL of 0.100 M CH3COOH 
and 50 mL of 0.100 M HCl, (d) A solution made by mixing 
100 mL of 0.100 M CH3COOK and 50 mL of 0.100 M KCl.

Accepted Answer

Hello everyone. So in this video we're going to be talking about different mixtures of buffers. So we have kind of a guide to follow when we're doing problems like this. So a bit above for consists of we have four different possible mixtures. Our 1st 1 is a weak base plus its conjugate acid. Or we could have a weak acid and its conjugate base. Or we could have a weak acid plus a strong base. But the acid must have a higher concentration then our base and our last and final possible mixture would be a weak base with a strong acid and of course the concentration of our base will have to be greater than the concentration of our asset. Okay so those are four possible choices. So let's go ahead and evaluate our forgiven mixtures then. So for eight we have an N A F. That's the salt of H F. Which is a weak acid. So this is going to be a base that we have N A B R. That we see here that's the salt of Hbr which is a strong asset. So N A b r is going to be neutral. So we have a base and we have something that's neutral. That's not one of our possible choices for a concoction of a buffer. So this one is definitely not a buffer. Then we move on to be. So for B we have first R h f H F is a weak acid. Alright so we have that let's look at the second possible um reagent. Just K O H K O H is a strong base. So we have the right blend. We have um a weak acid and a strong base but we need to take into account the concentration which is of course just looking at the volume as well. And of course we have to remember that the acid must be greater than the concentration of our base. So for our concentration of H. F. The given the concentration is 0.05 moller. And then for our K. O. H. R. Strong base against the same exact thing but the volume is different. So for H. F. Our weak acid were given or we have 50 million years of that and for R K. O. H we have at sea we have 1 milliliters. So actually then our concentration of H. F. Is less than the concentration of our strong base and therefore we don't have the right um concentrations for a buffer. So again we don't have a buffer so not a buffer. I'm gonna go ahead and actually scroll down a little bit to give us a little bit of more space. Let's move on to see. So for c we have again H. F. And we have said for this to be a weak acid, then we have K. B. R. This is a salt of Hbr we don't have a conjugate base of HF. So we have a salt of H. B. R. Which is not H. S. Conjugate base. So again we do not have a buffer. Now last option, we're gonna go back to color blue here we're working with um answer Tracy. Now again we have our H. F. We should be very familiar with this, this is not a weak acid or this is a weak acid and not a strong acid. And then we have our base of K. O. H. Which is a strong base. And so we have the right blend of free agents. So we have a weak acid and a strong base. But of course we have to go ahead and consider the concentrations and the volume as well. And of course for a buffer we need to have that the concentration of our weak acid is greater than the concentration of our strong base. So let's go ahead and evaluate this. So of course our concentration of R H F is given to us to be 0.50 moller. Then we have the concentration of R K O H R. Strong base given to us which is actually the same as our weak acid, but the volumes are different. So for HF we have 50 mL of R K O. H. We have 25 mL. So we can see that our concentration of our acid is going to be greater than the concentration of our strong base. And as a matter of fact that is a correct concoction and mixture of I buffer. So this one is a buffer. So going back to the answer choices A, B, C and D, the correct answer. And the only possible buffer is going to be answer choice D. And that's going to be my final answer for this problem.

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