[binosmith]

I tried to balance it according to my book but i don't understand how to balance the equation by oxidation method

equation:-

Cr2O7-- + Fe2++H+   ---> Cr3+ +Fe 3+ + H2O

[sundrops]

Balance it in two parts then add them together.

1. balance Fe2+ -> Fe3+
2. balance Cr2O7 -> Cr3+ + H2O
3. add/cancel any floating H+'s or H2O's

4. add everything together - watch your charges!

At least that's the way I remember doing it  
Hopefully it works out for you!

Just to get you started...

1. Fe2+ -> Fe3+ + e-

2. Cr2O7 -> Cr3+ + H2O
    Cr2O7 + 14H+ + 8e- -> 2Cr3+ 7H2O

now all you have to do is add them together and make sure the charges can cancel out - good luck.