You titrated Valine, dissolved it, solidified the solution with an excess of HCl

Question

You titrated Valine, dissolved it, solidified the solution with an excess of HCl, then titrated with NaOH until pH of 13.5 was reached. Use the following info to determine. a. Molecular weight of Valine and b. calculate pI (isoelectric point).
mass of valine: 0.203g
molarity of NaOH: 0.165 M
equivalence point 1: not seen
volume of p1: 18.39ml
volume at pka2: 24.21ml

7. 4 pointsl You titrate valine as we did with an eatesse the trated with NaOH untilapl of 11swas reached folowing information to determine: a The molecular weghtof valine Mass of Vaise o203 Melanie OTYagh 0.165M Guwalence paint Not seen Voluntea volume at 21

Explanation / Answer

Volume of NaOH used to reach pKa2 = 24.21 ml

So, the volume of NaOH needed to reach pKa1 = 24.21/3 = 8.07 ml

volume of NaOH to reach first equivalence point = 2 x 8.07 = 16.14 ml

moles of NaOH used = moles of valine present = 0.165 M x 16.14 ml = 2.663 mmol

a. molecular weight of valine = 0.203 g/2.663 x 10^-3 mol = 76.23 g/mol

b. pI of valine = 13.5/2 = 6.7

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