Q39 / 200 · WBJEE 2013 · Chemistry
The orange solid on heating gives a colourless gas and a green solid which can be reduced to metal by aluminium powder. The orange and the green solids are, respectively
- A$\mathrm{NH}_{4} \mathrm{Cr}_{2} \mathrm{O}_{7}$ and $\mathrm{Cr}_{2} \mathrm{O}_{3}$
- Correct answerB$\mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ and $\mathrm{Cr}_{2} \mathrm{O}_{3}$
- C$\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ and $\mathrm{CrO}_{3}$
- D$\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CrO}_{4}$ and $\mathrm{CrO}_{3}$
Solution
Orange solid is ammonium dichromate.
$\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \stackrel{\Delta}{\longrightarrow} \mathrm{N}_{2} \uparrow+\mathrm{Cr}_{2} \mathrm{O}_{3}+4 \mathrm{H}_{2} \mathrm{O}$
$$
\mathrm{Cr}_{2} \mathrm{O}_{3}+2 \mathrm{Al} \longrightarrow 2 \mathrm{Cr}+\mathrm{Al}_{2} \mathrm{O}_{3}
$$
Hence, the correct answer is option: 'B'.