Ni (s) + Cd^2+(aq)-->Ni^2+(aq)+ Cd(s)

Question

MnO4^-1(aq)+ Al (s) ---> Mn^2+(aq)+Al^3+(aq)

no matter what i do, i can't seem to balance either of these redox reactions. i'm always off. is there a trick to doing these? i need help please.

Answer 1

The Ni/Cd equation is balanced.
a. atoms balance.
b. charge balances.
c. gain and loss of electrons balance.

For the other one, Mn goes from +7 on the left to +2 on the right for 5e gained. Al goes from zero on the left to +3 on the right for 3 electrons lost. The LCD for 5 and 3 is 15 so use 5 for the Al coefficients and 3 for the Mn coefficients, then balance water and H^+.