which of the following indicators would be the best to use when 0.050M HA (Ka= 2
ID: 873948 • Letter: W
Question
which of the following indicators would be the best to use when 0.050M HA (Ka= 2.5*10^-6) is titrated with 0.05M NaOH?a. Bromophenol blue, pH 3.0-4.5 b. Bromcresol green, pH 3.8-5.4 c. Alizarin, pH 5.7-7.2 d. Phenol red, pH 6.9-8.2 e. Phenolphthalein, pH 8.0-10.1 which of the following indicators would be the best to use when 0.050M HA (Ka= 2.5*10^-6) is titrated with 0.05M NaOH?
a. Bromophenol blue, pH 3.0-4.5 b. Bromcresol green, pH 3.8-5.4 c. Alizarin, pH 5.7-7.2 d. Phenol red, pH 6.9-8.2 e. Phenolphthalein, pH 8.0-10.1 which of the following indicators would be the best to use when 0.050M HA (Ka= 2.5*10^-6) is titrated with 0.05M NaOH?
a. Bromophenol blue, pH 3.0-4.5 b. Bromcresol green, pH 3.8-5.4 c. Alizarin, pH 5.7-7.2 d. Phenol red, pH 6.9-8.2 e. Phenolphthalein, pH 8.0-10.1
Explanation / Answer
The indicator should have color change when equivalence point is reached.
Given Ka=2.5*10^-6
HA + NaOH -----> NaA + H2O
0.05 0.05 0 0
0 0 0.05 0.05
We know, Kw = KaKb. So Kb = 10E-14/2.5*10^-6 = 4E-9
NaA + H2O ---------> HA + NaOH
0.05 0 0
0.05 -x x x
Kb = 4E-9 = x2/ (0.05-x)
x = 1.4 E -5
pOH = -log x = 4.85
pH = 14 - pOH = 9.14
so, e. Phenolphthalein will show best results as it is in this pH range
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