Question

The quantity 432 mg of a monoamino monocarboxylic amino acid is observed to consume 7.39 mEq of acid and base in the titration range pH 0.8 to 12.0. What is the name of the amino acid?

Answer 1

The given information is not sufficient to apply Henderson-Hasselbalch .

Need to attempt it with other method, lets try it.

First write the equation for this reaction- H2A + 2NaOH → Na2A + 2H2O

Where A is the amino acid.

The equation states that 2 moles of base titrates 1 mole of amino acid.

As the change from pH 0.8 to pH 12.0 is the full titration that means the both the carboxyl group and the amino group are deprotonated, 7.39 mmol was used in the ionization of the entire amino acid.

So 3.70 mmol of amino acid was titrated by the 7.39 mmol of base.

Now we can obtain molecular weight by dividing the mass of the amino acid by the moles titrated:

432 mg amino acid/3.70mmolaminoacid = 117 mg /mmol or 117.151 g/mol

We know amino acid whose MW is 117 g/mol. Yes its Valine.

Also it fits the description of a monoamine monocarboxylic amino acid.