2a. Which indicator used for the titration of a string acid with strong base. I
ID: 561046 • Letter: 2
Question
2a. Which indicator used for the titration of a string acid with strong base.I am confused on why question 2a. was correct for g. Phenolphthalein. Please explain how the answer would not be f. Bromethymol Blue
2b. Which indicator used for the titration of 0.10M HCl agasint 0.10 NH3.
why would 2b not be g. Phenolphthalein 2. Which indicator should be chosen for the titration of the following: (6 pts) Indicator a. methyl violet b. thymol blue c. bromophenol blue d. methyl orange e. methyl red f. bromthymol blue g. phenolphthalein pH 0-2 1-3 3-5 2-3 4-6 6-8 8-10 12-14 o-10 PH 9.2( h. indigo sulfonate indicator used for the titration of a strong acid with a strong base. Na? hydFochloric acid against 0.1 indicator used for the titration of 0.10 M 0 ammonia. (Kb for NH 1.8x10-5) 3. The Equivalence Point of an Acid Ti-pa-q Posnt of an äeid9.2
Explanation / Answer
a.
Titration of a strong acid with a strong base, the titration curve is steepest at pH = 7, so phenolphthalein is used as indicator.
Bromothymol blue is a pH indicator, which is mostly used for neutral pH.
b) Indicator used for the titration of 0.10M HCl against 0.10 NH3.
First calculate the pH at pH at the equivalence point for the titration of 0.10 M HCl with 0.10 M NH3
Make an ICE table to find the equilibrium concentration of hydronium cation.
NH4+(aq) + H2O(l) NH3(aq) + H3O+(aq)
I 0.05 0 0
C –x +x +x
E 0.05 –x x x
Ka = 5.56 x 10^-10
Ka = [NH3][H3O+]/ [NH4+]
5.56 x 10^-10 = x^2/0.05
x^2 = 5.56 x 10^-10 x 0.05
= 2.78 x 10^-11
x = 5.27 x 10^-6 = [H3O+]
pH = - log [H3O+]
= - log (5.27 x 10^-6)
= 5.28
At this PH range, Thymol blue is good pH indicator
Phenolphthalein is pink in pH's between 8.2 and 12, and is colorless below pH 8.2, so it cannot be used.
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