Cr6++3e−→Cr3+Fe2+→e−+Fe3+Cr2O7−2+6e−→2Cr3+6Fe2+→6e−+6Fe3+
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Cr2O7−2+6Fe2+→2Cr3++6Fe3+
Now you must deal with the unbalanced O7 on the left. If you choose an acid medium you put H2O on the right and H+ on the left, like this:
Cr2O7−2+6Fe2++14H+→2Cr3++6Fe3++7H2O
If you choose a basic medium you put H2O on the left and OH- on the right, like this:
Cr2O7−2+6Fe2++7H2O→2Cr3++6Fe3++14OH−
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