How Can A Weak Acid Dissolve Glass?
Glass is one of those commonplace materials that we find everywhere. It has been used for both functional purposes (containers for liquids and solids) and artistic endeavors (many fine pieces of etched glass can be found in museums around the world). One of the values of glass is its relative chemical inertness. Materials such as concentrated hydrochloric or sulfuric acids can be stored in glass indefinitely. However, hydrofluoric acid will react strongly with a glass container.
Amazing But True
- In water, hydrochloric acid (HCl) is essentially completely dissociated. The protons in this acid are free to react readily with other materials. Hydrofluoric acid, on the other hand, is a weak acid, not completely ionized into H+ and F- ions. At room temperature, less than 10% of the compound exists in the ionized state.
- Glass is composed of silicon dioxide, a fairly unreactive material. However, glass is readily attacked by HF, but not by HCl. The process appears to involve HF molecules (not protons) that disrupt silicon-oxygen bonds in the glass.
- Hydrofluoric acid has a variety of uses. It can serve to remove rust in laundry products. Major industrial applications include purification of aluminum, electroplating, preparation of surfaces for silicon fabrication processes in electronics, and as a reagent in the synthesis of a wide variety of organic molecules that contain fluorine (such as Teflon).
- Watch a video dealing with the reaction between HF and glass: http://www.youtube.com/watch?v=K3g02t3O5QQ
With the links below, learn more about HF, weak acids, and glass. Then answer the following questions.
- Why is hydrogen fluoride’s boiling point so high?
- Why is the H-F bond hard to break?
- What organic compounds are resistant to HF?
- List four uses for HF in the academic environment.
- What is one material that can be applied to the skin in case of HF skin contact?