Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following attacks glass? (a) \(\mathrm{HCl}\) (b) \(\mathrm{HBr}\) (c) \(\mathrm{HI}\) (d) \(\mathrm{HF}\)

Step-by-Step Solution

Answer

The acid that attacks glass is (d) HF.

Step 1: Understanding the Chemical Properties of Glass

Glass is primarily composed of silicon dioxide (SiO₂). For an acid to attack glass, it must react with silicon dioxide. Not all acids have this ability, which will help us identify the correct answer.

Step 2: Consider Reactivity of Each Acid with Silicon Dioxide

Evaluate each acid: Hydrochloric acid (HCl), hydrobromic acid (HBr), and hydroiodic acid (HI) do not react with silicon dioxide. However, hydrofluoric acid (HF) reacts vigorously with silicon dioxide, forming hexafluorosilicic acid and water.

Step 3: Conclusion Based on Reactivity

Since only HF reacts with silicon dioxide, we determine that hydrofluoric acid is the acid that can attack glass.

Key Concepts

Silicon Dioxide

Silicon dioxide, known by its chemical formula SiO₂, is a major component of glass. It is a naturally occurring compound found in quartz and other minerals. This compound gives glass its durability and resistance to various chemical attacks. However, it is important to note that not all chemicals can interact with silicon dioxide due to its stable molecular structure. This stability grants glass a long-lasting lifespan in everyday applications.

• Silicon dioxide is also referred to as silica.
• It is commonly found on Earth, particularly in sand and rocks.
• Due to its solid state, SiO₂ contributes to the hardness of glass.

Understanding its properties is crucial when studying how different substances, especially acids, can interact with and alter silicon dioxide's structure.

Acid Reactivity

The reactivity of an acid refers to its ability to engage in chemical reactions. This quality varies significantly between different acids and depends on factors such as the strength of the acid and its concentration. When it comes to attacking glass, or more precisely, silicon dioxide, most acids, including hydrochloric (HCl), hydrobromic (HBr), and hydroiodic (HI) acids, do not have the capability to react with SiO₂.
However, these acids can react with other substances, showcasing their general reactive properties in different contexts.
In the case of glass:

• The inert nature of SiO₂ against many acids protects glass from most acidic environments.
• Understanding an acid's unique properties can predict its interactions with specific materials like silicon dioxide.

By knowing which acids can attack glass, we can better utilize and protect glass in various applications.

Hydrofluoric Acid

Hydrofluoric acid (HF) is an exceptional type of acid known for its ability to react with glass. Unlike other acids which leave silicon dioxide unaffected, HF has a distinctive chemistry allowing it to penetrate and dissolve SiO₂. This occurs because HF reacts with silicon dioxide to form hexafluorosilicic acid and water, effectively breaking down the glass structure.
This reactivity with SiO₂ makes HF extremely useful in industrial applications including glass etching and cleaning. However, it also requires careful handling due to its corrosive nature and potential health risks.
Important points about HF:

• HF is weaker than some acids in terms of ionization in water, but its chemical reactivity is unique.
• It is used in processes that require alteration or removal of glass/silica components.
• Safety protocols are paramount when working with HF due to its potential to cause severe chemical burns.

Understanding HF’s properties and its interaction with silicon dioxide is vital for safe and effective use in appropriate applications.