Acid-Base Titrations

General Chemistry lecture covering the use of titration for measuring the concentration of acid or base, and definitions of the end point and equivalence point of a titration. We explain the use of acid-base indicators for detecting the end point of a titration and how to compute the pH of solution at any point during a titration.

Category:

Education

Tags:

• General Chemistry
• acid
• base
• titration
• indicator
• end point
• equivalence point
• buffer solution

[893097011]

I still dont get the midpoint problem at 7:05. How did you get the concentration to be 0.067?

[chemdog8]

@893097011 The original concentration of benzoic acid in this calculation was 0.2 M. At the midpoint of the titration, half of the acid has been used up, so if the volume had not changed, the acid concentration would be 0.1 M. However, the addition of the base also increased the volume of solution by 50%, so the acid concentration is actually 0.2M / 2 / 1.5 = 0.067 M

[KnockoutMagic]

I NEED HELP if you can give it to me! What does happen to the pH during the titration if i'm using pheop....and methyl orange

[chemdog8]

@KnockoutMagic Hi. The pH changes rapidly during a titration as the equivalence point is reached. However, the range of pH for the color change depends on the indicator because the indicator is also an acid-base pair. See the wikipedia page on PH_indicator

[zut212]

I don't understand at 7:04. Specifically, how did you calculate that the Molarity (M) is 0.067? According to my calculation, I have M=(#moles HOBZ)/(TOTAL VOLUME) = (0.02moles HOBZ)/(0.150 L) = 0.01333 M

Keep in mind, that the number of moles of HOBZ is CONSTANT.

Why is your concentration value 50% mine?

[chemdog8]

At the midpoint of the titration, approximately half of the acid has been converted to base, so the nominal concentration will be 0.0133/2=0.067 M.  The system adjusts slightly from there to satisfy the equilibrium constant.

[ErinRuningen]

You're the bomb! Thanks for the great video.

[MaraboutVids]

@chemdog8 On the graph, the midpoint is 0.05, so why is it 1.5 L, shouldn't the new volume be 1.05L

[MaraboutVids]

thx .... helped me out for my biochem test prep

[mariov922432]

you had to put your picture in the beginning

[mingalabaa]

@chemdog8 Did you mean to type .133/2 = .067M?

[mingalabaa]

On the slide beginning at 2:52 min, , do you have typo in "50mL base"? Shouldn't it be "50mL acid" as you stated in your explanation?