Q: A student titrates an unknown amino acid with .1521 M NaOH andgets inflection

Question

Q: A student titrates an unknown amino acid with .1521 M NaOH andgets inflection points after adding 3.29 mL and 18.61 mL of tirant. Determine the concentration of the amino acid.
A: I think to determine the concentration of the amino acid, Ishould use the equation M1V1 = M2V2. My guess is that Ishould use the 18.61 mL value to calculate the AA concentration,but can someone tell me why? Thanks
A: I think to determine the concentration of the amino acid, Ishould use the equation M1V1 = M2V2. My guess is that Ishould use the 18.61 mL value to calculate the AA concentration,but can someone tell me why? Thanks

Explanation / Answer

The two inflection points indicate the first and second equivalencepoints. It shows that the amino acid is diprotic and the volumes ofNaOH given are those required for titration of each proton. The second volume - 18.61 mL is the volume required for completetitration of the amino acid. So it is taken as the finalequivalence point. Hence, V1 = 18.61 mL M1 = 0.1521 M . Volume of amino acid, V2 = 10 mL Concentration of amino acid, M2 = M1 V1 / V2                                                  = 0.1521 M * 18.61 mL / 10mL                                                  = 0.283 M

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