25ml of 1.5x10^-3 M nitrous acid (HNO2) is titrated with 1.2x10^-3 dichromate ion (Cr2O7^2-^). The titration is monitored with a potentiometer using a SCE reference electrode (Eref= 0.241V). the solution is buffered at ph=4.00. determine the potential of the solution when 9.00ml of Cr2O7^2-^ have been added

Cr2O762-^ (aq) + H^+^+ + e- ---> Cr3++ h2O (l) (not balanced) E^o^= 1.36V

NO3-(aq) + H^+^(aq) + e- ---> HNO2 (aq) + H2) (l) (not balanced) E^o^ = 0.940V