Question

Thermal decomposition of ammonium dichromate gives:
A.${{\text{N}}_{\text{2}}}$ , ${{\text{H}}_{\text{2}}}{\text{O}}$ and ${\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{3}}}$
B.${{\text{N}}_{\text{2}}}$ , ${\text{N}}{{\text{H}}_{\text{3}}}$ and ${\text{CrO}}$
C.${\left( {{\text{N}}{{\text{H}}_{\text{4}}}} \right)_{\text{2}}}{\text{Cr}}{{\text{O}}_{\text{4}}}$ and ${{\text{H}}_{\text{2}}}{\text{O}}$
D.${{\text{N}}_{\text{2}}}$ , ${{\text{H}}_{\text{2}}}{\text{O}}$ and ${\text{Cr}}{{\text{O}}_{\text{3}}}$
E.${{\text{N}}_{\text{2}}}$ , ${{\text{H}}_{\text{2}}}{\text{O}}$ and ${\text{CrO}}$

Answer 1

Hint: In ammonium dichromate, chromium is present in a $ + 6$ oxidation state. It consists of ammonium ions and dichromate ions. The chromium ion undergoes reduction in this reaction.

Complete step by step answer:
Ammonium dichromate is a bright orange or red colored crystalline solid. It is unstable thermodynamically. It ignites readily and burns producing a voluminous green residue of chromium oxide. If heated in a closed container, the container might rupture due to the decomposition of the material of the container due to the large amount of heat produced. It also acts as a strong oxidizing agent when mixed with or contaminated with a combustible material. Ammonium dichromate is soluble in water. The thermal decomposition of ammonium dichromate gives nitrogen gas, chromium (III) oxide and water vapour.
\[{\left( {N{H_4}} \right)_2}C{r_2}{O_7} \to {N_2} + C{r_2}{O_3} + 4{H_2}O\]
The thermal decomposition of ammonium dichromate crystals involves the occurrence of four consecutive reactions. The decomposition reaction is studied by means of differential thermal and thermogravimetric analysis. The nature of the intermediate compounds so formed is determined by the method of X-ray diffraction and by labeling by radioactive elements as tracers. The gases released are analyzed by the process of gas chromatography and potentiometric techniques.

The correct option is A.

Note:
This technique is widely used in pyrotechnics and was commonly used in the early days of photography as well as in lithography. Since it decomposes spontaneously and yields nitrogen gas, it is used as a source of pure nitrogen in the laboratory. It also has applications as a mordant for dyeing pigments, in the manufacturing of alizarin. Although, it is a very toxic compound and also potentially a carcinogen.