In one experiment a student titrated 25.00 mL of an acidic solution containing Cu^2+ and Zn^2+ with 0.0123 M NaOH. The midpoints of the three pH jumps occurred at 15.35 mL, 19,77 mL, and 22.05 mL of added base. What was the concentration, in mol/L and mg/L, of Cu^2+ and Zn^2+ in the original solution? If the solution was prepared by dissolution of 0.654 g of brass in 250.00 mL solution, what the percentage of copper and zinc in the original sample of brass