Question
Potassium dichromate is prepared from
A.
chromate obtained by the fusion of chromite ore with sodium carbonate in free access of air
B.
pyrolusite which is fused with potassium hydroxide in the presence of air
C.
iron pyrites by the fusion with potassium carbonate in presence of moisture
D.
none of these
Answer :
chromate obtained by the fusion of chromite ore with sodium carbonate in free access of air
Solution :
$$\mathop {4FeC{r_2}{O_4}}\limits_{{\text{Chromite ore}}} + 8N{a_2}C{O_3} + 7{O_2} \to $$ \[\underset{\begin{smallmatrix}
\text{Sodium chromate} \\
\left( \text{yellow} \right)
\end{smallmatrix}}{\mathop{8N{{a}_{2}}Cr{{O}_{4}}}}\,+2F{{e}_{2}}{{O}_{3}}+8C{{O}_{2}}\]
$$2N{a_2}Cr{O_4} + 2{H^ + } \to $$ $$N{a_2}C{r_2}{O_7} + 2N{a^ + } + {H_2}O$$
$$N{a_2}C{r_2}{O_7} + 2KCl \to $$ \[\underset{\begin{smallmatrix}
\text{Potassium} \\
\text{dichromate}
\end{smallmatrix}}{\mathop{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}\,+2NaCl\]