Question

Glass is soluble in:
A. $\text{HF}$
B. ${{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$
C. $\text{HCl}{{\text{O}}_{\text{4}}}$
D. Aqua regia

Answer 1

Hint: It is a hydrogen halide. Halides are the elements present in the Group-17 of the periodic table. These are fluorine, chlorine, bromine and iodine.
This hydrogen halide in solid-state remains in a zig-zag type of chain with intermolecular hydrogen bonding.

Complete step by step answer:
Glass, also known as water glass or soluble glass is soluble in$\text{HF}$.
The chemical name of the soluble glass is sodium silicate. It is composed of sodium oxide ($N{{a}_{2}}O$) and silica (silicon dioxide, $Si{{O}_{2}}$).
Fluoride ion of $\text{HF}$ attacks the silicon of $Si{{O}_{2}}$. Thus it forms a strong bond and weakens the silicon-oxygen lattice structure which is one of the main components of glass. Glass surface dissolves in the solution having enough amount of $\text{HF}$.
This principle is also used in the cleaning process of the silicon wafers with $\text{HF}$ in the semiconductor industry.
The reaction of $\text{HF}$ with glass is as follows:
$Si{{O}_{2}}+\text{ }4HF\to Si{{F}_{4}}+2{{H}_{2}}O$
Another reaction of $Si{{O}_{2}}$ with $\text{HF}$ is known as ‘etching of glass”. Here, gaseous or water-soluble silicon fluorides are formed which is used to polish glass.
$Si{{O}_{2}}+\text{ }4HF\to {{H}_{2}}Si{{F}_{6}}+2{{H}_{2}}O$
$Si{{F}_{4}}$ formed is not a solid and $Si{{O}_{2}}$ is a gas at room temperature.
HF is not a solvent since in this case, it reacts with the glass vessel.
So, the correct option is A.

Note: $\text{HF}$ is not a solvent by nature. This reaction with the glass is one of the exceptions. Water glass is named as such because it is silicon dioxide dissolved in water. After evaporation, the solution becomes solid glass. It is used for manufacturing acid-resistant cement.