How To Draw Titration Curve For Amino Acid

Objectives:

To determine the titration curve for an amino acid.
To use this curve to estimate the pKa values of the ionizable groups of the amino acid.
To understand the acid base behaviour of an amino acrid.

Theory:

Titration curves are obtained when the pH of given volume of a sample solution varies afterward successive addition of acid or alkali. The curves are usually plots of pH against the volume of titrant added or more than correctly confronting the number of equivalents added per mole of the sample. This curve empirically defines several characteristics. The precise number of each characteristic depends on the nature of the acid being titrated:

i) the number of ionizing groups, 2) the pKa of the ionizing group(s), 3) the buffer region(s).

Fig: 1: Titration bend

Amino Acids are weak Polyprotic Acids. They are nowadays equally zwitter ions at neutral pH and are amphoteric molecules that can be titrated with both acid and alkali. All of the amino acids have an acidic group (COOH) and a basic group (NH_ii) attached to the α carbon, and besides they contain ionizable groups that act as weak acids or bases, giving off or taking on protons when the pH is altered.

The stiff positive charge on the amino grouping induces a tendency for the carboxylic acrid group to lose a proton, so amino acids are considered to exist potent acids. Some amino acids have other ionizable groups in their side chains and these tin also be titrated.

When an amino acid is dissolved in water information technology exists predominantly in the isoelectric grade. The isoelectric signal, pI, is the pH of an aqueous solution of an amino acid at which the molecules take no cyberspace charge. In other words, the positively charged groups are exactly balanced by the negatively charged groups. When this dissolved amino acid is titrated with acrid, information technology acts equally a base, and with base, it acts as an acrid which makes them an amphoteric molecule.

These ionizations follow the Henderson-Hasselbalch equation:

When the concentration of the unprotonated form equals that of the unprotonated class, the ratio of their concentrations equals 1, and log 1=0. Hence, pKa can be defined as the pH at which the concentrations of the protonated and unprotonated forms of a item ionizable species are equal. The pKa also equals the pH at which the ionizable grouping is at its best buffering chapters; that is the pH at which the solution resists changes in pH most finer.

The pK is the pH at the midpoint of the buffering region (where the pH changes but slightly upon addition of either acrid or base). The pK is the pH corresponding to the inflection point in the titration curve. The terminate point of a titration bend represents the observed end of the titration.
The isoelectric point (isoelectric pH; pI) is the pH at which the amino acid has a net zero charge. For a unproblematic diprotic amino acrid, the pI falls halfway between the 2 pK values. For acidic amino acids, the pI is given past ½(pK1 + pK2) and for bones amino acids it's given by ½(pK2 + pK3).

In this experiment we are finding out the titration curve of the amino acid Glycine.

Glycine is a diprotic amino acid which ways that it has two dissociable Protons, one on the α amino group and the other on the carboxyl group. In the case of Glycine,the R group does non contribute a dissociable Proton.

The dissociation of proton proceeds in a certain society which depends on the acerbity of the proton: the i which is most acidic and having a lower pKa will dissociate beginning. And so, the H+ on the α-COOH group (pKa1) volition dissociate before that on the α-NH3 group (pKa2).