Cu+HNO2-Cu(NO3)2+NO solved by oxidation no. Method
You made a typo. You meant HNO3 and you omitted H2O as one of the products.
Cu + HNO3-Cu(NO3)2 + NO + H2O
Cu on left has oxidation number 0; on right is +2. N on left is +5 and on right is +2 (in NO) and for the moment ignore the NO3 ion in Cu(NO3)2.
So multiply the Cu change by 3 and the N change by 2 to make 6 electrons lost and gained; that gives you
3Cu + 2HNO3 --> 3Cu(NO3)2 + 2NO + H2O
That balances the oxidation-reduction part. Now you notice there are 6 NO3^- in which the N did NOT change so add 6 more to the HNO3 on the left to handle that. Now the equation is
3Cu + 8HNO3 --> 3Cu(NO3)2 + 2NO + H2O and then balance the H by making H2O 4. Done.
3Cu + 8HNO3 --> 3Cu(NO3)2 + 2NO + 4H2O
To solve the given chemical reaction using the oxidation number method, follow these steps:
Step 1: Assign oxidation numbers to each element in the reaction.
In this case, we have:
Cu + HNO2 → Cu(NO3)2 + NO
The oxidation number of Cu is 0 because it is an uncombined element.
The oxidation number of H in HNO2 is +1.
The oxidation number of N in HNO2 is +3.
The oxidation number of O in HNO2 is -2.
Step 2: Determine the element undergoing oxidation and reduction.
Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number.
In this case, Cu goes from an oxidation number of 0 to +2 in Cu(NO3)2. So, Cu is undergoing oxidation.
N goes from an oxidation number of +3 to +2 in NO. So, N is undergoing reduction.
Step 3: Balance the charges by adding electrons.
Since Cu is undergoing oxidation, we write the oxidation half-reaction as follows:
Cu → Cu2+ + 2e-
Since N is undergoing reduction, we write the reduction half-reaction as follows:
N3+ + 3e- → N2+
Step 4: Balance the number of electrons in both half-reactions.
To balance the electrons, multiply the oxidation half-reaction by 3 and the reduction half-reaction by 2:
3Cu → 3Cu2+ + 6e-
2N3+ + 6e- → 2N2+
Step 5: Combine the half-reactions.
Add the two half-reactions together:
3Cu + 2N3+ → 3Cu2+ + 2N2+
Step 6: Balance the remaining elements.
Balance the remaining elements, in this case, the nitrogen atom and the nitrogen oxide:
3Cu + 2N3+ → 3Cu2+ + 2N2O
Step 7: Write the final balanced equation.
The balanced equation for the reaction is:
3Cu + 2HNO2 → 3Cu(NO3)2 + 2NO
By following these steps, you can solve this reaction using the oxidation number method.