Question

In: Chemistry

Which of these indicators would be appropriate for the following titrations. Methyl Orange pKa = 4.1...

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

Solutions

Expert Solution

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


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