[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

[777888]

merry x'mas
can somebody help me? thanks

[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]

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.

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

[777888]

Q1

Quote jdurg:
"For strong acid and strong base titration, any indicator can be used. It is because the sharp pH change at the equivalent point."
 
 
"Absolutely correct.  With a strong acid and strong base titration, the end point is where the pH = 7.00 (Neutral).  As soon as you add one more drop of NaOH, the pH will shoot up into the basic range since NaOH is a strong base.  (And the addition of one drop to a neutral solution will cause a huge increase in the OH- concentration).  So while you're titrating, the solution will be clear until it suddenly becomes basic due to that addition of one extra drop of NaOH."