Question

When finely powdered silica is mixed with a magnesium powder and heated in fire-clay crucible to compounds are formed which are:

• A. magnesium oxide and silica
• B. oxygen and magnesium silicate
• C. magnesium dioxide and crystalline silicon
• D. magnesium dioxide and amorphous silicon

Answer 1

The correct option is D magnesium dioxide and amorphous silicon

Finely powdered silica (sand or quartz) is mixed with magnesium powder and heated in a fire- clay crucible. Magnesium oxide and silicon are formed. The product is washed with dilute hydrochloric acid to dissolve magnesium oxide, a basic impurity. Then it is washed with hydrofluoric acid to remove unreacted silica. The powder left behind is silicon its amorphous form.

$Si{O}_2+2Mg⟶Si+2MgO$