# How do I balance the reaction equation of zinc and nitric acid?

How would you balance the following reaction using the oxidation number method? $$\ce{Zn + HNO3 -> Zn(NO3)2 + NH4NO3 + H2O}$$

My approach:
Half reactions:
\begin{align} \ce{Zn &-> Zn(NO3)2} & \text{Change in oxidation state of }\ce{Zn} &= 2\\ \ce{2HNO3 &-> NH4NO3}& \text{Change in oxidation state of }\ce{N} &= 8\\ \end{align}

Multiplying by the L.C.M of the change of the oxidation number. \begin{align} \ce{4Zn &-> 4Zn(NO3)2}\\ \ce{2HNO3 &-> NH4NO3} \end{align}

Adding them, $$\ce{4Zn + 2HNO3 -> 4Zn(NO3)2 + NH4NO3}$$

I don't know how to proceed further.

Am I going wrong in any of the above steps? (Please don't convert the reactants and products to ions, and solve it using the method that I am using, so that I can identify my mistake)

• Your half reactions are not balanced, that's the problem. – Ivan Neretin Nov 30 '17 at 10:24
• I have updated your post with chemistry markup. If you want to know more, please have a look here and here. We prefer to not use MathJax in the title field, see here for details. – Martin - マーチン Nov 30 '17 at 11:10
• You should convert the reactants and products to ions to identify what actually changes. And you must not not forget the electrons! $\ce{Zn -> Zn^2+ +2e-}$, etc. – Martin - マーチン Nov 30 '17 at 11:16
• But my book says when writing half reactions in oxidation number method, only the atoms whose oxidation number changes should be balanced. Well, that's what I did. – Piano Land Nov 30 '17 at 11:23
• Still, try to balance the half-reactions before adding them together. I believe that's the easier way. – Ivan Neretin Nov 30 '17 at 11:32