Question

Which of the following is the green coloured powder produced when ammonium dichromate is used in fireworks?
(A) Cr
(B) $ Cr{O_2} $
(C) $ C{r_2}{O_3} $
(D) $ CrO({O_2}) $

Answer 1

Hint :The inorganic compound ammonium dichromate has the formula $ {\left( {N{H_4}} \right)_2}C{r_2}{O_7} $ . Chromium is in a +6 oxidation state in this compound, as it is in other chromates and dichromates. This is known as hexavalent chromium. It's a salt that's made up of ammonium and dichromate ions.

Complete Step By Step Answer:
Because of its usage in tabletop "volcano" displays, ammonium dichromate is sometimes referred to as Vesuvian Fire. However, due to the carcinogenic nature of the substance, this display has grown controversial in schools. It was also utilised in the early days of photography and in pyrotechnics. It has been used in pyrotechnics, lithography, as a source of pure nitrogen in the laboratory, and as a catalyst since the early days of photography. It's also employed in the production of alizarin, chrome alum, leather tanning, and oil purification as a mordant for colouring colours. When ammonium dichromate is used in fireworks, a green powder is created. $ C{r_2}{O_3} $
 $ {\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}\quad \mathop \to \limits^\Delta {\text{C}}{{\text{r}}_2}{{\text{O}}_3} + {{\text{N}}_2} + 4{{\text{H}}_2}{\text{O}} $
It has the same thermodynamic instability as ammonium nitrate. Once started, the decomposition reaction completes, yielding a large amount of dark green powdered chromium(III) oxide. In this process, not all of the ammonium dichromate decomposes. When the green powder is dissolved in water, leftover ammonium dichromate produces a yellow/orange solution.
Hence option C is correct.

Note :
During a kinetic examination of the heat decomposition of ammonium dichromate, observations acquired using relatively high magnification microscopy revealed that salt breakdown occurs with the participation of an intermediate liquid phase rather than a solid phase.