12. Solving a chemistry problem

4. To 10 ml of ZnCl2 solution was added 2 ml of 10-2 M Na3HY and 1 ml of acetate buffer. Excess Na3HY was titrated with 10-2 M CuSO4 solution from a microburet and the following potentiometric titration data was obtained.
VCuSO4, ml 0.50 0.75 1.00 2.25 1.50 1.75 2.00
E, mV 403 400 392 375 327 320 318
Determine the end point of the titration by the first derivative and calculate the concentration of Zn2 ions, in g/l.