The pH titration curve applies to the titration of 40.0 mL of a 0.100 M solution of an acid with 0.100 M NaOH. What are the approximate pKa values for this acid?

(a) pKa1 = 5, pKa2 = 10 (b) pKa1 = 7, pKa2 = 11 (c) pKa1 = 5, pKa2 = 10, pKa3 = 13 (d) pKa1 = 5, pKa2 = 7, pKa3 = 10

Video transcript

Hello everyone today. We are being asked the following question. The curve below shows the hydration of a dia protic acid with sodium hydroxide, estimate the P. K. Values for this dye protic acid. So the first thing we want to make note of is that this is di protic and di means two. That means we're gonna have not only to P. K. S, but we're gonna have to equivalent points. Now equivalence points are essentially just when the molds of our acid are equal to the moles of our base and they can be represented by vertical lines. So we see that our volume at our first equivalence point, It's going to be at 50 Mila leaders. If we were to examine this further, we would see that our second one is going to be at 100 Mila leaders. So the volume at our second equivalence point Is at 100 Mila leaders. By definition the P. K. A. It's going to be the ph or half the ph it's gonna be the ph that is half of the first equivalence point. And so if we look at half of 50 ml because that's our first equivalence point, half of 50 is 25 Mila leaders. And this is gonna be where our first P. K. Is. So if we go to 25 mL, that's gonna take us right to about 2.5. So our first p. K. value will be 2.5. Moving on, we're gonna do the same thing with our second P. K. Are you Our 2nd p. K. A. value. If we look at this, the second PK value is gonna be the ph that is halfway between our first two And so if we have 50 and 100 halfway is going to be 75 mila leaders. So if you look at the ph at 75 ml that's gonna give us our second peak A value 75 mm. That is going to be Roughly 6. as our final answer. And with that we have our two PK values and we have solved the problem overall, I hope this helped and until next time.