Question

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

Answer 1

Hint: In the given compounds when ammonium dichromate that is given as ${(N{H_4})_2}C{r_2}{O_7}$ is
heated then oxygen is not produced instead of oxygen ammonium dichromate on heating
produces nitrogen gas.

Complete step by step answer:
For option A.)
In this option, $KCl{O_3}$ is known as potassium chlorate and when potassium chlorate is heated
Then potassium chlorate decomposes and forms potassium chloride and oxygen gas. This
reaction is done in the presence of manganese dioxide as a catalyst. This reaction can be
represented as:
$2KCl{O_3}\xrightarrow{\Delta }2KCl + 3{O_2}$
For option B.)
 In this option, $Zn{(Cl{O_3})_2}$ is known as zinc chlorate. When zinc chlorate is heated then it decomposes to give zinc chloride and oxygen. This reaction can be represented as:
$2Zn{(Cl{O_3})_2}\xrightarrow{\Delta }ZnC{l_2} + 3{O_2}$
For option C.)
In this option, ${K_2}C{r_2}{O_7}$ is known as potassium dichromate. When potassium dichromate is heated then it decomposes and gives potassium chromate, chromic oxide and oxygen in the products. This reaction can be represented as:
For option D.)
In this option, ${(N{H_4})_2}C{r_2}{O_7}$ is known as ammonium dichromate. When ammonium dichromate is heated then it forms nitrogen gas, chromic oxide and water. This reaction can be represented as:
${(N{H_4})_2}C{r_2}{O_7}\xrightarrow{\Delta }{N_2} + C{r_2}{O_3} + 4{H_2}O$
As we can see that all the above compounds give oxygen when they are heated except the ammonium dichromate (${(N{H_4})_2}C{r_2}{O_7}$) which gives nitrogen gas on heating and not produce oxygen gas.
Hence, option D.) is the correct answer.


Note:
Always remember that chlorates are ionic compounds containing the chlorate anion ($Cl{O^{ - 3}}$) and the cation of a metal and when they are heated then they decompose to produce oxygen gas and a metal chloride as given in option A) and B).