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ii) To determine the effect, in terms of change in pH of the solution, of adding a strong base (NaOH) to both a strong acid (HCl) and a weak acid (CH3COOH) solution.
iii) To generate the ‘true’ titration curve for the amino acid, alanine, showing the neutralization of the acid by added base and the change in pH during the titration. ... Based on the graphs, a negative logarithmic (to base 10) relationship was found to exist between pH and [H+], an association further confirmed by Figure 1(b), i. ... The pH of the solutions at every addition of the strong base was recorded (Table 2 and 3), and plotted against volume of NaOH added. The titration curves for HCl and CH3COOH are shown in Figure 2. With the HCl/NaOH system, the titration curve began at a very low pH of 1.0, as HCl is a strong acid, and ended at a high pH typical of a strong base. There was a large rapid change in pH with a small addition of the base near the equivalence point (pH = 7). For the CH3COOH/NaOH system, the titration curve began at a higher acidic pH, due to the weak nature of acetic acid and ended at a higher basic pH. ... The pKa of acetic acid was found to be 4. ... When pH was near the pKa, the addition of OH- changed the pH of the acetic acid solution only gradually until the acid was mostly neutralized as very little conjugate acid was left to buffer the addition of base. The change in pH was smallest at the pKa (when the acid was half neutralized) indicating that this point had the highest buffer capacity. ... The data were then combined to generate a complete titration curve for alanine (refer to Figure 3). ... 00 with addition of acid and pH 12 with addition of base. Combining the pH data recorded in Table 5 and 7 for the titrations of water with both HCl and NaOH, a complete titration curve was generated (Figure 3).
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