In: Chemistry
Which of these indicators would be appropriate for the following
titrations.
Methyl Orange pKa = 4.1
Bromthymol Blue pKa = 7.0
Phenolphthalein pKa = 9.3
ethylamine titrated with hydrochloric acid
perchloric acid titrated with lithium hydroxide
formic acid titrated with sodium hydroxide
sodium acetate titrated with nitric acid
The best indicator is the one whose pKa matches with the pH of the titration at equivalence point.
A) Titration of ethylamine with HCl
The conjugate acid of a weak base is a strong acid. So the pH at equivalence point would be acidic.
The indicator which is best for this would be thus,
Methyl orange with pKa = 4.1
B) perchloric acid titration with LiOH
Both perchloric acid and LiOh are strong acid and strong base, respectively.
Thus the pH at equivalence point would be +7 neutral
The best indicator for this titration would be,
Bromothymol Blue pKa = 7.0
C) Formic acid titrated with NaOH
Titration of weak acid as formic acid with strong base NaOH
The conjugate base of weak acid is a strong base. So the solution would be basic at equivalence point.
The best indicator for this titration would be,
Phenolphthalein
D) Sodium acetate with nitric acid
At equivalence point the pH of this solution would be slightly acidic.
The best indicator for this titration would be,
Methyl orange pKa = 4.1