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Name: Rafal Haleem Student Number: 301160786 Partner: Kirzia POST-LAB QUESTIONS 1. On the basis of titration data, why might it be difficult to distinguish between lysine and tyrosine? It is difficult to distinguish Lysine and Tyrosine using titration because both of them have similar pKa values. pKa1 of Lysine-2.18 PKa1 of Tyrosine-2.20 pKa2 of Lysine-8.95 pKa2 of Tyrosine-9.11 2. What is the pH of each of these solutions? (a)10-3 M HNO3 (b) 6.21  10-4 M HCl pH of 6.21 × 10-4 M HCl Strong acids ionize completely at dilute aqueous solutions. So, Ka of that acid is unity. Now given, concentration of H+ is 6.21 × 10-4 pH = - log10 [H+] = - log ( 6.21 × 10-4 ) = 3.20 So, pH of 6.21 × 10-4 M HCl is 3.20 HNO3 or nitric acid is a strong acid and it dissociates completely into aqueous solutions. Given, [H+] = 10-3 pH = - log [H+] = - log ( 10-3 ) = 3 pH of 10-3 M HNO3 is 3. 3. Write the appropriate equilibrium (see Equation 5) for each pKa of glycine and of your unknown.

Name: Rafal Haleem Student Number: 301160786 Partner: Kirzia

4. Define how many acid dissociation constants (pKa) a lysine has based on Table 1. How would you calculate the isoelectric point (pI) for lysine based on provided values? Lysine has 3 acid dissociation constants (pKa) based on table 1 pKa –COOH

pKa – NH3+

pKa R-Group

2.18

8.95

10.53

pI = (8.95 + 10.53)/2 pI = 9.74

5. The prevailing structure of the molecule in the one of the unknown amino acid solutions used in the experiment before titrating with NaOH is:

Name: Rafal Haleem Student Number: 301160786 Partner: Kirzia

What is the structure after the amino acid is titrated with NaOH? Already answered and handed in 6. Why the magnetic stirrer is not supposed to hit the pH meter electrode? Because the pH meter is very fragile and any object that hits it will result in the reading change. And might disturb the data. 7. Consider the amino acid having pKa’s of 3.90 and 9.90. What is its pI? Already answered and handed in 8. Why it is important to calibrate the pH meter before the titration? A membrane in the pH meter allows H+ ions to pass through, allowing a current to flow and generating a voltage. The meter measures the voltage, and you tell it which normal buffer it should be in. To calculate the pH of your solution, the pH meter compares the voltage of your unknown solution to that of the buffers....