Titration of weak acids - KSU Faculty

Titration of weak acids Titration of amino acids Amino acids are weak polyprotic acids . Neutral amino acids are (gly, ala, threonine ) are treated as diprotic acids . acidic amino acids (glu, asp,) are treated as triprotic acids . Basic amino acids (lys , arg , his ) are treated as triprotic acids . pHm is the pH at which the maximum total number of charges present. Glycine can be obtained in three forms : a) Glycine hydrochloride c)Sodium glycinate

b) Isoelectric glycine Titration of amino acids Example: Calculate the pH of a 0.1M solution of a) Glycine hydrochloride , b) Isoelectric glycine , c)Sodium glycinate Ka1 = 4.57 x 10-3

a) Glycine hydrochloride is a diprotic acid , the carboxylic group is a much stronger acid than the amino group , the pH of the solution is dependent exclusively by the extent the carboxyl group ionizes . , assume y = [ AA+1] that ionizes . Thus, y = [H+] produced, and y = [AA] produced . AA+1 remaining at equilibrium = [ AA+1] original - [ AA+1] that ionizes = 0.1 y Thus, =4.57 x 10-3

Titration of amino acids Since amount of y (value of y) is stronger than that can be ignored , Thus 4.57 x 10-4 - 4.57 x 10-3 y = y y 2 2 + 4.57 x 10-3 y - 4.57 x 10-4 = 0.0

Y , where a = 1 , b = 4.57 x 10-3 , c = 4.57 x 10-4 Thus y = [H+ ] = 1.92 x 10-2 . pH = 1.72 . What is the degree of ionization of glycine hydrochloride in this 0.1M solution ? b) The pH of AA is the pI ( the pI is defined as that pH where the predominant ionic form is AA , so net charge on the amivo acid is zero .) So pH = = 5.97 c)Sodium glycinate is a diprotic base ,

Both the unionized amino group and the carboxylate ion can accept a proton from water , but since the amino group is a much stronger base than the carboxylate group , the pH of the solution depends almost exclusively on the extent to which amino group ionizes . Titration of amino acids For the amino group : Kb1 =x10-5 For carboxylate group ; Kb2 =x10-12 Kb1 =

[OH- ] [AA ] = (y) (y) Kb1 = Because the concentration of sodium glycinate is much larger than K b1 thus y can be neglected from the dominator . Titration of amino acids

3.98 x10 5 = , so y2 = 3.98 x 10 6 y= y = 1.99 x 10 3 M , [OH ] = 1.99 x 10 3 M [H+] = 5 x 10 12 M pH = -log[H+ ] = 11.3 . Titration Curve of Neutral Amino Acids Amino acids are titrated in exactly the same manner as diprotic and triprotic weak acids . Neutral amino acid

Titration Curve of Acidic amino Acid (Glutamate ) Titration Curves of Lysine Titration Curves of Amino Acids Information that can be obtained from a titration curve : 1- The number of ionizable groups in that amino acid , which can be detected from the number of titration stages in the curve , (or the number of pK a s or number of flat zones in the curve) . 2-Whether the triprotic amino acid is basic or acidic , that can be detected from the pKa 2 . If its value is closer to the value of pKa 1 (that of the carboxyl group ), then it is an acidic amino acid .

If the value of its pKa2 is closer to the value of pKa 3 (that of the aminogroup ), then it is basic amino acid . 3- The pKa values of the amino acid can be obtained from the curve which is equal to the pH value at the mid-point . 4- The isoelectric point , pI for each amino acid can be obtained from the curve by detecting the point where the amino acid is all in the zwitterion form (net charge = 0.0) the pH at that point is the pI . Or it can be obtained mathematically from ; pI = pKa1 + pKa2 ( in the case of a neutral amino acid ) . 2 In the case of triprotic amino acids , the pI is calculated from :

pI = pKa1 + pKa2 2 ( in the case of acidic amino acids ) . Titration Curves of Amino Acids pI = pKa2 + pKa3 in the case of basic amino acids. 2 5- You can also determine from the curve the pH values at which the amino acid can act as a

buffer . (the pH ranges 1 from the pH value of each midpoint). How to Obtain a Titration Curves of Amino Acids No of moles of weak acid or a.a Calculate the first moles of OH by A= Calculate the second moles of OH added B= No of moles of weak acid or a.a + A Calculate the third moles of OH added C= No of moles of weak acid or a.a + B

How to Obtain a Titration Curves of Amino Acids Sketch the pH curve for the titration of 100ml of 0.1M Glycine with KOH? Pka1=1.71, Pka2=9.6? No of moles of a.a = M*V = 0.1 * 0.1 =0.01 mole The first moles of OH by A= 0.01 / 1.71 = 0.005 The second moles of OH added B= 0.01 + 0.005 = 0.015 PI = (Pka1 + pka2)/ 2 =5.66 Plot the titration curve of Aspartic acid it has a volume of

100ml and0.1M When titrated with 0.1M KOH? Pka1=2.09, Pka2=3.86, Pka3=9.82? Plot the titration curve of Lysine which has a volume of 200ml and 0.3M When titrated with 0.1M NaOH? ? Pka1=2.18, Pka2=8.95, Pka3=10.35?

Recently Viewed Presentations

• This data is the first piece of information the search engine finds. Since PDF files are TEXT (unless scanned and not captured as text), search engines will do a full text search on the documents. Search Results Search Criteria A:...
• DECA members become: academically prepared. for college and careers in marketing, finance, hospitality or management. community oriented. by gaining an appreciation for the benefits of service and their potential impact on the community and world. ... Autodesk Certified User Exam.
• Using the Form Wizard. Another method of building a form is to use the Form Wizard tool. The Form Wizard allows you to: Select the fields that will appear on the form. Choose the form layout (which determines the positioning...
• Restitution des expertises * * * * EPICOH - Bergen * The French cohort consists of five thousand and ninety eight miners. The inclusion criteria are the following: … In the cohort, there are some exposed miners and some non...
• You have been imagining yourself in scenarios in schools. In doing this you have been seeing yourself being closer in role to the teacher than the pupil.
• Saisie des noms des enseignants par discipline et par classe terminale en vue de la saisie des appréciations en ligne (AEL) Saisie du nom du professeur principal (Suivi des candidatures des élèves) Du 20 janvier au 20 mars . 2016....
• Resources consistent with HQDA priorities GWOT / ONS TRADOC Modularity Reset The Force Overarching guidelines Cross level internally Use available excess equipment external to the transforming units (including pre-positioned sets and depot stocks) Consider "in lieu of" equipment where the...
• Law regulates the public and private institutions that are a central part of our lives Law is a word of many meanings— it is difficult to define Law and Justice Definitions of law do not necessarily include justice Justice is...