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CBSE Class 11-science Answered

magnesium reacts with nitric acid to give magnesium nitarate and nitrous oxide gas and liquid water  balance this by oxidation number method
Asked by govtsecschoolnayaganv051 | 19 Aug, 2018, 06:29: PM
Expert Answer

1.       Find out the element which undergoes a change in oxidation number:

The oxidation number of Mg increases from 0 to +2 in Mg metal to Mg(NO3)2 and N decrease from +5 in HNO3 to +1 in N2O

 2.       Find out the total increase/decrease in oxidation number :

Total Increase in Mg is 2 and decrease in N is 4 but there are two N atoms in N2O and one in HNO3. Hence, the decrease in Oxidation number of N is 2 X 4 =8

3.       Balance increase/decrease in Oxidation number:

Since the total increase is 2 and decrease  is 8.thereore, multiply Mg on LHS by 4 and combine step 2 and 3

Hence equation will be written as :

4 Mg(aq) +2 HNO3(aq) → Mg(NO3)2 (aq) + N2O (g)+ H2O

4.       Balance all atoms other than O and H:

To balance Mg on either side, multiply (MgNO3) by 4 we have,

4 Mg +2HNO→ 4 Mg (NO3)2+N2O+H2O

Now there are 10 N atoms on RHS and 2 on LHS, therefore to balance N atoms change the coefficients of HNO3 from 2 to 10 on LHS and we have,

4 Mg(NO3)2+10HNO3 → 4 Mg (NO3)2+N2O+H2O

5.       Balance O and H :

There are 30 O atoms on LHS but only 26 atoms on RHS, therefore, to balance O atoms, change the coefficients of H2O from 1 to 5. We have,

4 Mg(NO3)2+2HNO3 → 4 Mg (NO3)2+N2O+5H2O

Here H atoms get balanced automatically.

Answered by Ramandeep | 20 Aug, 2018, 04:36: PM
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