Question

Consider the following reaction and based on the reaction answer the questions that follow:

$\begin{array}{r}{\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\stackrel{\text{heat}}{⟶}{\mathrm{N}}_2(\mathrm{g})+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{Cr}}_2{\mathrm{O}}_3\\ \end{array}$

Calculate:
The quantity in moles of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ if $63g$ of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ is heated.

Answer 1

• Weight of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$:

$$\begin{gathered} =(14+4)\times 2+52\times 2+16\times 7 \\ =18\times 2+52\times 2+16\times 7 \\ =36+104+112=252 \end{gathered}$$

• $252\mathrm{g}\text{represents}1\text{mole}$
• $1\text{g represents}\frac{1}{252}\text{mole}$
• $63\mathrm{g}\text{represents}\frac{1}{252}\times 63=\frac{1}{4}\text{mole}$$=0.25\text{mole}$
• Therefore, the quantity in moles of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ if $63g$ of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ is heated is $0.25$ mole.