Question

Glass reacts with HF to produce: (a) \(\mathrm{H}_{2} \mathrm{SiF}_{6}\) (b) \(\mathrm{Na}_{3} \mathrm{AlF}_{6}\) (c) \(\mathrm{H}_{2} \mathrm{SiO}_{3}\) (d) \(\mathrm{SiF}_{4}\)

Short answer

The correct product is (d) SiF_4 .

Step-by-step solution

Understanding Glass Composition

Glass primarily comprises silicon dioxide (SiO_2 ). This is essential as it determines how it reacts chemically with other substances, such as hydrofluoric acid (HF).

Reaction Between SiO2 and HF

When silicon dioxide (SiO_2 ) reacts with hydrofluoric acid (HF ), it results in the formation of silicon tetrafluoride (SiF_4 ) and water (H_2O ). The reaction is as follows: \[\mathrm{SiO}_2 + 4\mathrm{HF} \rightarrow \mathrm{SiF}_4 + 2\mathrm{H}_2\mathrm{O}. \]

Identifying the Product from the Options

Based on the reaction, the main product formed is silicon tetrafluoride (SiF_4 ). Reviewing the options given: (a) H_2SiF_6 , (b) Na_3AlF_6 , (c) H_2SiO_3 , (d) SiF_4 . Option (d) matches the product SiF_4 from our reaction.

Key concepts

Silicon Dioxide Reactivity

Silicon dioxide, often referred to as silica, is a major component of glass and many types of minerals. It is chemically represented as \( \mathrm{SiO}_2 \). What makes silicon dioxide particularly interesting is its unique reactivity, primarily due to the robust covalent bonds between silicon and oxygen atoms within its structure. However, despite its strength, \( \mathrm{SiO}_2 \) can still react under specific circumstances.
In general, silicon dioxide is quite stable, demonstrating resistance to most acids. The key exception is its reaction with hydrofluoric acid (\( \mathrm{HF} \)). This reactivity is unique because \( \mathrm{HF} \) can break the strong silicon-oxygen bonds. The result is a transformation, leading to different chemical products. Understanding this interaction is vital, especially in industrial applications where controlling glass degradation is crucial. The capacity of \( \mathrm{SiO}_2 \) to react with \( \mathrm{HF} \) is a primary reason for the careful handling of both substances.

Hydrofluoric Acid Reaction

Hydrofluoric acid (\( \mathrm{HF} \)) is a powerful and somewhat infamous chemical due to its ability to dissolve glass and silica-related materials. This ability stems from the reactive nature of the fluoride ion (\( \mathrm{F}^- \)). Let's look deeper into what happens during the reaction of \( \mathrm{HF} \) with silicon dioxide (\( \mathrm{SiO}_2 \)).
The reaction can be succinctly expressed by the equation:
\[ \mathrm{SiO}_2 + 4\mathrm{HF} \rightarrow \mathrm{SiF}_4 + 2\mathrm{H}_2\mathrm{O} \]
This indicates that each molecule of \( \mathrm{SiO}_2 \) reacts with four molecules of \( \mathrm{HF} \) to yield a molecule of silicon tetrafluoride (\( \mathrm{SiF}_4 \)) and water. \( \mathrm{HF} \) excels at breaking the \( \mathrm{Si-O} \) bonds due to the strong affinity between silicon and fluoride ions. It's fascinating that a simple reaction like this dramatically alters the material's properties and composition. Practices involving \( \mathrm{HF} \) must always consider safety, both for chemical handling and resulting environmental reactions.

Silicon Tetrafluoride Formation

The formation of silicon tetrafluoride (\( \mathrm{SiF}_4 \)) is a significant chemical transformation, especially noted in reactions involving glass and \( \mathrm{HF} \). This outcome provides evidence of \( \mathrm{SiO}_2 \) reactivity in environments where it normally remains stable. Let's understand the outcome of this specific reaction.
Silicon tetrafluoride is a gaseous compound formed through the meeting of \( \mathrm{SiO}_2 \) and \( \mathrm{HF} \), represented by:
\[ \mathrm{SiO}_2 + 4\mathrm{HF} \rightarrow \mathrm{SiF}_4 + 2\mathrm{H}_2\mathrm{O} \]
This reaction not only exemplifies an acid-base reaction (\( \mathrm{HF} \) acting as a Lewis acid accepting electrons), but it also spotlights the considerable alteration from a solid, quartz-like substance to a gaseous state. Silicon tetrafluoride can further react with water, emphasizing the compound's reactive nature within various contexts of chemistry. Understanding \( \mathrm{SiF}_4 \) formation is crucial, especially in industrial applications where glass etching and surface treatments are part of essential processes.