We can approximate the pH at this point. All of the a-COOH has been deprotonated (pK, 2.10) but none of the R-COOH has been deprotonated (pK. - 3.86). charge on the amino acid at this point is zero. This is the isoelectric point of aspartic acid, the pH at which it will precipitate out of solution. The average of these two pK, values is close to the observed pH: (2.10 + 3.86)/2 = 2.98. Overall, the The next significant point in the titration is the second half-way point, when pH - pk of the R-COOH group. OH 8. What is the pH of the second half-way point for aspartic acid? 50% H H HN CH HAN CH 0- 50% pH- It would take an addition of 1.5 equivalents (1.5 moles) of OH' gives this pH. 9. What is the new charge on aspartic acid at this pH? Charge at 2.10 - 10. Draw the structure of aspartic acid (or insert a drawn image) at the second equivalence point and determine its charge and the pH of the solution. Image or drawing here pH Charge 11. Draw the structures, distribution, and charge of aspartic acid at pH=9.82