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The findings of a biochemistry lab experiment at Birzeit University, where students investigated the pH and titration curves of various amino acids. The experiment aimed to determine the pKa values and isoelectric points (pI) of these amino acids by titrating them with sodium hydroxide. The students recorded the pH changes and plotted the titration curves, providing insights into the amphoteric nature and dissociation of the amino acids' functional groups.
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to determine the ph for certain amino acids after adding a strong base (NAOH), and the curves of it. know the changes that occur to the PH and it’s reason(studying the affect of strong base on amino acid regarding the PH and its behavior).
Amphoteric substanc e is a substance can act as base and acid (it’s act as base in presence of acid and act as acid in presence of base ), amino acids is one of the amphoteric substance , amino acid are organic molecule that composed of amino group NH3,R group, carboxyl group COO- , its function to form the proteins. The pka, pI values can be determined by the Titration technique, titration it’s a process by which the base is added to the acid slowly until the solution become base.
Sodium hydroxide (100Mm) Amino acids( 100mM of glycine, histidine, and lysine, 50 Mm glutsmic acid, ph<2) PH meter Burettes (10ml)
Glycine: because the concentration of glycine is greater than the concentration of NaOH, there will be more H+ ions at first. At pH(pka1)=2.8, so the carboxylic group of glycine begins to donate its H+ ion to OH-, neutralizing NaOH, the pH will stay constant in this time, The addition more amount of NaOH raises the pH, and glycine becomes a "zwitterions" when it has both positive and negative charges. The NH2 group of glycine begins contributing H+ at the pH(pka2) = 9.6, so The pi was 6. Lysine: When we added the hydroxide to the solution, the concentration of hydroxide is increase and the hydrogen ion concentration decreases, depending on the curve, the pka1 (2.2) is expresses the dissociated of carboxyl group(faster) ,, the pka2(=9)is expresses the dissociate of an amino acid, pka3 (=10.3) is expresses the R group dissociation, so the pi = 9. Histidine: The concentration of histidine is greater than the NAOH concentration, so The carboxylic group of histidine begins to donate its H+ to OH- at pH= 2.3 ( pKa1), neutralizing NaOH.. The more addition of NaOH raises the pH, and histidine becomes a "zwitterions" becaus e it’s has a positive and negative charges (the net charge=0) The NH2 group begins to donate the H+ at pKa2=9.2, pkr=6. so the pI is 7. Alinine: When we add the hydroxide to the solution the concentration of hydroxide is increace and the H+ is decreases, then. The carboxyl group is dissociate pka1=2.4, then the alpha amino is dissociate and the pka2= 9.8, so the pi was 6.1, so the alinine has a negativly charged -1. Glutamic acid: The dissociative of the carboxyl group is cause the pk1 and pkr , when we added the naoh the R group is neutralization , glutamic acid has a negatively charged. Conclusion :
