Question

Which of the following does not give oxygen on heating?
\[
  A.{\text{ }}KCl{O_3} \\
  B.{\text{ }}Zn{\left( {Cl{O_3}} \right)_2} \\
  C.{\text{ }}{K_2}C{r_2}{O_7} \\
  D.{\text{ }}{\left( {N{H_4}} \right)_2}C{r_2}{O_7} \\
 \]

Answer 1

Hint: In order to solve the given problem we will first understand the basic chemical name of each of the compounds further we will see the chemical reaction each of the compound undergoes in the process of heating with the help of chemical equation. Further on the basis of the chemical reaction we will find which of the given compounds does not give oxygen on heating.

Complete step by step answer:
Option A is \[KCl{O_3}\] . Its chemical name is potassium chlorate.
Option B is \[Zn{\left( {Cl{O_3}} \right)_2}\] . Its chemical name is zinc chlorate.
Option C is \[{K_2}C{r_2}{O_7}\] . Its chemical name is potassium dichromate.
Option D is \[{\left( {N{H_4}} \right)_2}C{r_2}{O_7}\] . its chemical name is ammonium dichromate.

In order to find the compound which does not release the oxygen on heating we will see the chemical reaction each of the compound undergoes on heating one by one.
For option A or potassium chlorate; the reaction it undergoes on heating is as follows:
\[2KCl{O_3}\xrightarrow{\Delta }2KCl + 3{O_2} \uparrow \]
From the above reaction it is clear that when potassium chlorate is heated potassium chloride is formed and also oxygen gas is released.

For option B or zinc chlorate; the reaction it undergoes on heating is as follows:
\[Zn{\left( {Cl{O_3}} \right)_2}\xrightarrow{\Delta }ZnC{l_2} + 3{O_2} \uparrow \]
From the above reaction it is clear that when zinc chlorate is heated zinc chloride is formed as product and also oxygen gas is released.

For option C or potassium dichromate; the reaction it undergoes on heating is as follows:
\[4{K_2}C{r_2}{O_7}\xrightarrow{\Delta }4{K_2}Cr{O_4} + 2C{r_2}{O_3} + 3{O_2} \uparrow \]
From the above reaction it is clear that when potassium dichromate is heated potassium chromate and chromium oxide is formed as a product and also oxygen gas is released along with it.

Now let us see for option D.
For option D or ammonium dichromate; the reaction it undergoes on heating is as follows:
\[{\left( {N{H_4}} \right)_2}C{r_2}{O_7}\xrightarrow{\Delta }C{r_2}{O_3} + 4{H_2}O + {N_2} \uparrow \]
From the above reaction it is clear that when ammonium dichromate is heated chromium oxide and water is formed as a product and also nitrogen gas is released along with it but there is no release of oxygen gas.
Amongst the given options all the compounds are oxygen rich but only ammonium dichromate is not oxygen so each one of them releases oxygen whereas ammonium dichromate releases nitrogen on heating.
Hence, \[{\left( {N{H_4}} \right)_2}C{r_2}{O_7}\] does not give oxygen on heating.
So, the correct answer is “Option D”.

Note: In order to solve such types of problems students must remember the reaction that the compound undergoes under various conditions and in various chemical reactions. In pyrotechnics and in the early days of photography, ammonium dichromate was used as a source of pure nitrogen in the laboratory and as a catalyst, as well as in lithography. In the manufacture of alizarin, chrome alum, leather tanning and oil purification, it is also used as a mordant for dyeing pigments.