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titraton check

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777888:
I did some lab questions, can somebody see if I am right?! THANKS! :)

Q1: What pH indicators could be used to indicate the endpoint of a titration of a storng acid with a strong base?

MY ANSWER: Any indicator that has a pH range that falls in the vertical part of the titration curve. For example, bromothymol blue, phenolpthalein, phenol red, p-nitrophenol.

Q2: 50.0mL of 0.1 M CH3COOH is titrated with 0.3 M NaOH. Find the region of the titration curve (weak acid/strong base) where the change in pH is relatively small when NaOH is added(buffer region). Explain why this region would be a buffer? Is there an equivalenct region on the strong acid/strong base titration curve?
NOTE: the equilvalence point is where 16.7mL of NaOH is added.

MY ANSWER: The buffer region of the weak acid/strong acid titration curve is the region between 5.5mL and 12.5mL of NaOH is added(around halfway to the equivalence point. This region is buffer because:
CH3COOH + NaOH -> H2O + NaCH3COO
CH3COOH + OH- -> H2O +CH3COO-   (net ionic)
The small amount of OH- added is completely consumed and it converts a small amount of CH3COOH to CH3COO-. The overall effect is a small decrease in the amount of CH3COOH and a small increase in the amount of CH3COO-. Thus, there is only a slight increase in the pH. There isn't an equivalent region on the strong acid/strong base titration curve.

THANK YOU :D

777888:
merry x'mas
can somebody help me? thanks :D

Donaldson Tan:
Q1. The equivalent point of titration of a strong acid and strong base is pH 7. Use an indicator that changes colour near or at pH 7.

Q2: the buffer region would be where [H+] = [acetate]

AWK:
Buffre region will be start at [acetic acid/[acetate] 10/1 and end at 1/10 (1.5 to 15,2 ml of NaOH)

777888:

--- Quote from: geodome on December 26, 2004, 06:27:19 PM ---Q1. The equivalent point of titration of a strong acid and strong base is pH 7. Use an indicator that changes colour near or at pH 7.

--- End quote ---

but near the equivalence point, the curve is so steep (vertical), would something like phenolpthalein, phenol red also work?
thanks

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