Answer to Question #159372 in General Chemistry for Andrea Nicole Billardo

Question #159372

Balance the reaction in acid and base medium using half reaction method


Cr2O7-2 + Fe+2 - Cr+3 + Fe+3


1
Expert's answer
2021-01-29T08:30:10-0500

Solution:

Cr6++3eCr3+Fe2+e+Fe3+Cr2O72+6e2Cr3+6Fe2+6e+6Fe3+Cr^{6+}+3e^-\rightarrow Cr^{3+}\\Fe^{2+}\rightarrow e^- +Fe^{3+}\\Cr_2O_7^{-2}+6e^-\rightarrow 2Cr^{3+}\\6Fe^{2+}\rightarrow 6e^-+6Fe^{3+}


_______________________


Cr2O72+6Fe2+2Cr3++6Fe3+Cr_2O_7^{-2}+6Fe^{2+}\rightarrow 2Cr^{3+}+6Fe^{3+}

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:


Cr2O72+6Fe2++14H+2Cr3++6Fe3++7H2OCr_2O_7^{-2}+6Fe^{2+}+14H^+\rightarrow 2Cr^{3+}+6Fe^{3+}+7H_2O


If you choose a basic medium you put H2O on the left and OH- on the right, like this:


Cr2O72+6Fe2++7H2O2Cr3++6Fe3++14OHCr_2O_7^{-2}+6Fe^{2+}+7H_2O\rightarrow 2Cr^{3+}+6Fe^{3+}+14OH^-



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