Question:
In the leaching of alumina from bauxite, the ore expected to leach out in the process by reacting with $\mathrm{NaOH}$ is :
Correct Option: , 4
Solution:
In bauxite impurities of $\mathrm{Fe}_{2} \mathrm{O}_{3}, \mathrm{TiO}_{2}$ and $\mathrm{SiO}_{2}$ are present, $\mathrm{Fe}_{2} \mathrm{O}_{3}$ and $\mathrm{TiO}_{2}$ are basic oxides therefore does not reacts with or dissolve in $\mathrm{NaOH}$ whereas $\mathrm{SiO}_{2}$ is acidic oxide it gets dissolve in $\mathrm{NaOH}$, hence leach out $\mathrm{SiO}_{2}+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_{2} \mathrm{SiO}_{3}$ (aq.) $+\mathrm{H}_{2} \mathrm{O}$
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