Elemental silicon is oxidized by ${\mathrm{O}}^2$ to give a compound which dissolves in molten ${\mathrm{Na}}_2{\mathrm{CO}}_3$ . When this solution is treated with aqueous hydrochloric acid, a precipitate forms. What is the precipitate?

Elemental silicon is oxidized by ${\mathrm{O}}^2$ to give a compound which dissolves in molten ${\mathrm{Na}}_2{\mathrm{CO}}_3$. When this solution is treated with aqueous hydrochloric acid, ${\mathrm{SiO}}_2$. precipitate is formed.

$\mathrm{Si}+{\mathrm{O}}_2\to {\mathrm{SiO}}_2$

${\mathrm{SiO}}_2+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{Na}}_2{\mathrm{SiO}}_3$

${\mathrm{Na}}_2{\mathrm{SiO}}_3+aq\cdot \mathrm{HCl}\to \left(\text{ ppt) }\mathrm{NaCl}+{\mathrm{H}}_2{\mathrm{O}}_{+}+{\mathrm{SiO}}_2\right.$