500 mL of 0100 M NaH2PO4 1000 mL of 00500 M KOH 2000 mL of 0

        50.0 mL of 0.100 M NaH₂PO₄

        100.0 mL of 0.0500 M KOH

        200.0 mL of 0.0750 M HCl

        50.0 mL of 0.150 M NaCN

        Determine the volume of 0.100 M HNO₃ that must be added to the mixture to achieve a final pH value of 7.21.

Solution

KOH + NaCN -> KCN + NaOH 5 7.5 0 0 0 2.5 5 5 HCl + NaH2PO4 --> H3PO4 + NaCl 5 7.5 0 0 0 0 5 5 Total Volume = 50 +100 +200 +50 + x = 400 +x => (15-5 +0.1*x )/(400+x) = 10^-7.21 solving this... x= 100