Question

Which of the following does not give oxygen on heating ?

• A. ${ (NH_4)_2Cr_2O_7 }$
• B. ${KClO_3 } $
• C. ${ Zn(ClO_3)_2} $
• D. ${K_2Cr_2O_7 } $

Answer 1

The Correct Option is A

To determine which compound does not release oxygen upon heating, we need to analyze the thermal decomposition reactions of each compound:

1. { (NH_4)_2Cr_2O_7 }: This compound undergoes thermal decomposition to give nitrogen gas, water vapor, and chromium(III) oxide:
   { (NH_4)_2Cr_2O_7 \rightarrow N_2 + 4H_2O + Cr_2O_3 }
   Notice that the decomposition does not produce oxygen.
2. { KClO_3 }: This compound decomposes on heating to produce potassium chloride and oxygen gas:
   { 2KClO_3 \rightarrow 2KCl + 3O_2 }
   This clearly releases oxygen.
3. { Zn(ClO_3)_2 }: Similar to potassium chlorate, zinc chlorate decomposes to yield zinc chloride and oxygen gas:
   { Zn(ClO_3)_2 \rightarrow ZnCl_2 + 3O_2 }
   This also releases oxygen.
4. { K_2Cr_2O_7 }: While this compound itself does not undergo decomposition to release oxygen directly, it can further react in other reactions allowing for oxygen release. However, its direct thermal decomposition does not produce oxygen gas alone:
   { K_2Cr_2O_7 \rightarrow K_2CrO_4 + Cr_2O_3 + O_2 }
   It can potentially produce oxygen indirectly, especially when reacting with other oxidizing conditions.

The correct answer, based on our investigation, is: { (NH_4)_2Cr_2O_7 }, as it decomposes into nitrogen, water, and chromium(III) oxide without releasing oxygen gas.