Question

The different stages of preparing amorphous silicon are given below.
I. Silica is finely powdered.
II. The product is washed with hydrochloric acid.
III. The mixture of powdered silica and magnesium is heated in a fire-clay crucible.
IV. The product is washed with hydrofluoric acid to remove unchanged silica.
The correct arrangement of the above stages is :

• A. I, III, II and IV
• B. I, II, III and IV
• C. IV, I, II and III
• D. I, IV, III and II

Answer 1

The correct option is A I, III, II and IV

Amorphous silicon extraction process:

• Finely powdered silica is mixed with $Mg$ powder and the mixture is heated in a fire clay crucible.
• The products obtained are magnesium oxide and silicon.
• The product is then washed with dilute $HCl$ to dissolve magnesium oxide which is present as a basic impurity.
• Then, to remove the unreacted silica it is washed with hydrofluoric acid.
• The powder then left behind is silicon in its amorphous form.
• So, the correct order is $I,III,II$ and $IV$.