Stiochiometry - Advanced Higher, Help please!??

Question

25ml of a solution of sodium nitrite was acidified then titrated with 0.1mol per litre potassium permanganate. If 12.5ml were required for reaction and the half-equation for nitrite oxidation is:

N02¯ + H20 → N03¯ + 2H(one positive charge) + 2e¯

What is the concentration of sodium nitrate, in mol per litre to 3 decimal places.

10pts awarded to correct answer with clear working, thanks in advance :)

Answer 1

NO2- + H2O ------>  NO3-  +2H+  +2e-

MnO4-  -+ 5e---------->  Mn2+  

n°eqKMnO4 = n°eqNaNO2

N=z*M   z=5              N(KMnO4) = 5*0.1M = 0.5N

neqKMnO4 = 0.5eq/l*0.0125l=0.00625eq=n°eqNaNO2

N(NaNO2) = n°eqNaNO2/V= 0.00625eq/0.025l=0.25N

N=z*M   M=N/z   z=2    M=0.25/2=0.125M