2. What is the reduction half-reaction for the following unbalanced redox equation?

Question

Cr2O7^2– + NH4^+ Cr2O3 + N2

A.) Cr2O3 -> Cr2O7^2–
B.) Cr2O7^2– -> Cr2O3
C.) NH4^+ -> N2
D.) N2 -> NH4^+
I think it is B...?

3. Which oxidation-reduction reactions are best balanced by the half-reaction method?

A.) covalent reactions
B.) acid-base reactions
C.) ionic reactions
D.) intermolecular reactions
I think it is C....?

Answer 1

With practice you will learn what oxidizes and what reduces. To help let me give you the oxidation states and you figures these out for yourself.
Cr is +6 on the left and +3 on the right.
N is -3 on the left and zero on the right.

For the second question, AFTER you have balanced the reactions as far as change of electrons is concerned, don't you usually add H^+ (if acid) or OH^-(if base) and water? So what's the answer.