Problem 22 - Chemistry in 30 days

Question

Glass is soluble in (a) HF (b) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{HClO}_{4}\) (d) Aqua-regia

Step-by-Step Solution

Answer

Glass is soluble in HF (hydrofluoric acid).

Step 1: Identify the Composition of Glass

Glass is primarily composed of silica, which is silicon dioxide (SiO_2). Understanding the composition is key to determining which chemical agents can dissolve it.

Step 2: Review the Chemical Properties of Each Option

Examine the properties of each chemical: - Hydrofluoric acid (HF) is known for its ability to dissolve silicates and glass due to its reactivity with silicon dioxide. - Sulfuric acid (H_2SO_4) is a strong acid but does not generally attack glass. - Perchloric acid (HClO_4) is strong, but also does not affect glass. - Aqua regia, a mixture of hydrochloric and nitric acid, is used to dissolve noble metals, not glass.

Step 3: Determine the Correct Option

Since HF is specifically known to react with and dissolve silica (SiO_2), it is the option that makes glass soluble. The other acids do not have the same reactivity towards glass.

Key Concepts

Silicon Dioxide Solubility

Silicon dioxide, also known as silica, forms the primary component of glass and is known for its stability. Under normal conditions, silicon dioxide does not dissolve in water, acids, or bases, which makes glass resistant to many chemical processes. However, this does not mean it is completely insoluble under all conditions. Its solubility can be influenced by factors such as pH level, temperature, and the presence of certain solvents or acids. It is important to note that pure silicon dioxide is much more resilient compared to the complex mix found in glass. In specific chemical interactions, like with hydrofluoric acid, silicon dioxide can indeed be dissolved, leading to changes in the glass structure.

Hydrofluoric Acid Interaction

Hydrofluoric acid (HF) is unique due to its ability to react with silicon dioxide, the main component of glass. This reaction is one of the few chemical processes capable of breaking down silicon dioxide effectively. When HF interacts with silicon dioxide, it forms silicon tetrafluoride gas and water, with possible formation of hexafluorosilicic acid if there's enough HF present:\[ \text{SiO}_2 + 4\text{HF} \rightarrow \text{SiF}_4 + 2\text{H}_2\text{O} \]This reaction illustrates why HF is used in glass etching and cleaning processes where dissolution of glass is desirable. However, it is important to handle HF with caution due to its highly corrosive nature, posing risks of severe burns and systemic toxicity upon exposure.

Composition of Glass

Glass is an everyday material with unique properties, boasting a widespread use from windows to laboratory equipment. Its primary constituent is silicon dioxide (SiO extsubscript{2}), though it is rarely just pure silica. Typical glass is actually a complex mix of ingredients blended together to tailor its properties:

• Silicon dioxide (SiO extsubscript{2}) - provides structure, hardness, and chemical durability
• Sodium oxide (Na extsubscript{2}O) - lowers the melting point for easier processing
• Calcium oxide (CaO) - enhances chemical resistance
• Various metal oxides - impart color and improve specific properties

The careful balance of these components determines the glass’s interaction with chemicals. For example, soda-lime glass, one of the most common types, is not only affordable but also resists most chemical attacks, except by HF. The inclusion of different additives diversifies glass applications, from safety glass to high-tech screens.