balance redox equation

ok so ive balanced like alot of these redox equations but for some reason i cant get this one correct... H3PO2 + Cr2O72-  H3PO4 + Cr3+....

i get 6H3PO2 + 4Cr2O7 -2 +32H+ yields 6H3PO4+8Cr3+ +16H2O

but thats wrong..so idk if im making a mistake somewhere?

Try separating the reactions into half reactions using
1 Balance oxygen by adding water
2. Balance hydrogen by adding H+ ions
3. Balance charge by adding electrons

Then to join the equation, make sure the electrons balance.

PO23- + 2H2O----->PO43- + 4H+ + 4e-

Cr2O72- + 14H+ + 6e- ------>2Cr3+ + 7H2O

Adjust electrons and add

3PO23- + 6H2O + 2Cr2O72- + 28H+ + 12e- ------> 3PO43- + 12H+ + 12e- + 4Cr3+ + 14H2O

3PO23-  + 2Cr2O72- + 16H+  ------> 3PO43- + 4Cr3+ + 8H2O

This can be readjusted to make it look more like the original
3H3PO2 + 2Cr2O72- + 16H+ ------> 3H3PO4 + 4Cr3+ + 8H2O

Chat with an Online Tutor
Get help immediately by chatting with an live tutor right now



If you find this answer useful please share it with other students.