Titration curves KSU滴定曲线KSU.pptVIP

Titration curves Titration of a strong acid When a strong acid is titrated with a strong base the pH at any point is determined solely by the concentration of un titrated acid or excess base. The conjugated base that is formed has no effect on pH. Titration of a weak acid Weak acid dissociates in aqueous solution partially to give a small amount of H+ ions. HA H+ + A- When OH- ions are added during titration it is neutralized by H+ ions to produce H2O. The removal of the H+ ions disturbs the equilibrium thus more HA molecules will ionize to produce H+ ions to reestablish the equilibrium. This process will continue until all the HA molecules are ionized. Titration curve of a monoprotic weak acid 1 2 3 4 5 6 7 8 9 PH ml of 0.1M KOH added b c a d e NOTICE: When the acid is less than half titrated the pH is less than pKa When the acid is half titrated the pH = pKa When the acid is more than half titrated the pH is greater than pKa Titration of amino acids Dissociation of the α-amino group; When the α-carboxyl group is fully titrated the additional base added will start titrating the α-amino group which is a weaker acidic group pka = 9.1 compared to the α-carboxylic group which which explains it being titrated after the α-carboxylic group , thus dissociating and donating a proton to the enviroment leading to the formation of –NH2 or form III, which carries a net negative charge. Titration of amino acids Titration curve of glycine ; a) At point(a) predominant form is the fully protonated form. b) At point (b) 50% of the a.a is in the fully protonated form and 50% in the zwitterions form . At this point the concentration of the conjugated acid is equal to the concentration of the conjugated base and pH= pKa1 (pKa of α-carboxylic group) Point( b) represents the midpoint Where half of the α-carboxylic group is titrated. At the midpoint buffering behavior is maximum. Titration of amino acids c) At point (c) the predominating fo