Determination Of An Unknown Amino Acid From Titration Essay -- essays

Determination of An Unknown Amino Acid From TitrationAbstract test 11 used a titration curve to determine the identity operator operator of anunknown amino chemical group deadly. The initial pH of the solution was 1.96, and the pKasfound experimentally were 2.0, 4.0, and 9.85. The accepted pKa values werefound to be 2.10, 4.07, and 9.47. The molecular weight was calculated to be176.3 while the accepted value was found to be 183.5. The identity of theunknown amino acid was established to be glutamic acid, hydrochloride.IntroductionAmino acids are simple monomers which are strung together to form polymers(also called proteins). These monomers are characterized by the general twist shown in figure 1.Fig. 1Although the general structure of all amino acids follows figure 1, the presenceof a zwitterion is made possible due to the basic properties of the NH2 groupand the acid-forming properties of the COOH group. The amine group (NH2) is Lewisbase because it has a lone electron pair which makes it susceptible to acoordinate covalent bond with a hydrogen ion. Also, the carboxyl groupic group is aLewis acidic because it is able to donate a hydrogen ion (Kotz et al., 1996).Other forms of amino acids also exist. Amino acids may exists as acidic orbasic salts. For example, if the glycine reacted with HCl, the resulting aminoacid would be glycine hydrochloride (see fig. 2). Glycine hydrochloride is anexample of an acidic salt form of the amino acid. Likewise, if NaOH were added,the resulting amino acid would be sodium glycinate (see fig. 3), an example of abasic salt form.Fig. 2Fig. 3Due to the nature of amino acids, a titration curve can be employed to identifyan unknown amino acid. A titration curve is the plot of the pH versus the hoi polloiof titrant used. In the case of amino acids, the titrant will be some(prenominal) an acidand a base. The acid is a useful tool because it is able to add a proton to theamine group (see fig. 1). Likewise the base allows for removal of the protonfrom the carboxyl group by the addition of hydroxide. The addition of thestrong acid or base does not necessarily yield a drastic jump in pH. The acidor base added is unable to contribute to the pH of the solution because theprotons and hydroxide ions donated in solution are busy adding protons to theamine gr... ...unded series of unadulterated estimates which wererequired. Likewise, the deviance of the calculated molecular weight can beattributed to these crude vehicles, because the change in volume (between equivalence points) were used in calculation.ConclusionThe identity of an unknown amino acid was determined by establishing atitration curve. The equivalence and half-equivalence point, the pKa values,and the molecular weight were directly or indirectly found through the titrationcurve. The equivalence points were found through a crude method known as thetrapezoidal method. The establishment of the equivalence points gave rise tothe half equivalence point s and the D volume (used in calculating the molecularweight). The half-equivalence points were directly used to find the pKa valuesof the unknown. The molecular weight could also be calculated. This data led tothe determination of the identity of the unknown amino acid--glutamic acid,hydrochloride.ReferencesJicha, D. Hasset, K. Experiments in General Chemistry Hunt Dubuque, 199137-53.Kotz, J.C. Treichel , P. Jr. Chemistry and Chemical Reactivity Harcourt-BraceFort Worth, 1996 816-837.