Strong heating of zinc nitrate crystals causes dehydration followed by decomposition to zinc oxide with release of nitrogen dioxide and oxygen.
Explanation
Zinc nitrate commonly exists as hydrates such as Zn(NO3)2·6H2O. When heated, the water of crystallization is driven off first, yielding anhydrous Zn(NO3)2. With further heating, the nitrate decomposes to zinc oxide and gaseous nitrogen dioxide and oxygen according to the simplified reaction: 2 Zn(NO3)2 → 2 ZnO + 4 NO2 + O2. The solid residue becomes white zinc oxide, while brown NO2 gas is evolved. The process should be performed in a well-ventilated area or fume hood due to the toxic NO2 gas.
Key Points
- 1, The hydrated zinc nitrate loses water of hydration first, forming anhydrous Zn(NO3)2.
- 2, Upon stronger heating, Zn(NO3)2 decomposes to ZnO with evolution of NO2 and O2 (e.g., 2 Zn(NO3)2 → 2 ZnO + 4 NO2 + O2).
- 3, Observations include the release of water vapor during dehydration, brown NO2 gas during decomposition, and a white ZnO solid residue; NO2 is toxic and should be handled with proper ventilation.