8.2Composition of Glass and Its Uses
Glass is a versatile manufactured substance widely used in architectural structures, laboratory equipment, optical instruments, and everyday household items. When silica is heated together with other chemicals, various types of glass with distinct characteristics are formed.
Learning Objectives
- Describe briefly with examples the type of glass, their composition, properties and uses.
Mind Map of the 4 Main Types of Glass
A clear comparison of compositions, unique properties, and specific applications for each type of glass.
| Type of Glass | Composition | Key Properties | Uses |
|---|---|---|---|
| Fused Silica Glass | Silica only, \(\text{SiO}_2\) | High melting point, around \(1800\ ^\circ\text{C}\); minimal expansion or contraction | Telescope lenses |
| Soda-lime Glass | \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{CaCO}_3\) | Melts around \(1000\ ^\circ\text{C}\); easily moulded; cracks under sudden temperature change | Bottles and jugs |
| Borosilicate Glass | \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{CaCO}_3\), \(\text{B}_2\text{O}_3\), \(\text{Al}_2\text{O}_3\) | High heat resistance; low expansion coefficient; resists thermal stress | Laboratory beakers and flasks |
| Lead Crystal Glass | \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{PbO}\) | Soft, dense, heavy; high refractive index | Prisms |
Brief Explanation
Understand how different glass compositions create different properties.
1. Fused Silica Glass
Made from pure \(\text{SiO}_2\) without adding any other chemical. It requires a very high melting temperature of around \(1800\ ^\circ\text{C}\) and has minimal thermal expansion, making it ideal for precision lenses such as those in telescopes.
2. Soda-lime Glass
Made from \(\text{SiO}_2\), soda \(\text{Na}_2\text{CO}_3\), and limestone \(\text{CaCO}_3\). Soda lowers the melting point of silica to around \(1000\ ^\circ\text{C}\), making it easily moulded into bottles and jugs, but it cracks easily under sudden temperature changes.
3. Borosilicate Glass
Made from \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{CaCO}_3\), boron oxide \(\text{B}_2\text{O}_3\), and aluminium oxide \(\text{Al}_2\text{O}_3\). Its low expansion coefficient prevents thermal shock cracking, making it suitable for laboratory beakers and flasks.
4. Lead Crystal Glass
Made from \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), and lead(II) oxide \(\text{PbO}\). Lead replaces calcium to produce glass that is softer, denser, heavier, and has a high refractive index, making it suitable for prisms.
| Basic Property of Glass | Description |
|---|---|
| Hard but brittle | Glass is hard, yet it can break or shatter easily when struck. |
| Chemically inert | Glass does not react easily with most chemicals. |
| Transparent | Light can pass through glass, making it useful for windows and lenses. |
| Waterproof | Glass does not allow water to pass through it. |
| Heat insulator | Glass is a poor conductor of heat. |
| Electrical insulator | Glass does not conduct electricity. |
Try to Answer First
Answer mentally, then check the explanation.
What is the main component present in all types of glass?
Why can borosilicate glass be taken out from a refrigerator and heated directly without cracking?
What is the function of soda (\(\text{Na}_2\text{CO}_3\)) in the production of soda-lime glass?
Common Mistakes
Avoid these errors when comparing the types of glass.
Concept Misunderstandings
Compare each misconception with the correct fact.
All types of glass expand and contract significantly when heated.
Fused silica glass and borosilicate glass have very low coefficients of thermal expansion, meaning they barely expand or contract upon heating, preventing thermal cracking.
Soda-lime glass and fused silica glass have the same melting point.
Fused silica glass has a very high melting point of around \(1800\ ^\circ\text{C}\), while the addition of soda (\(\text{Na}_2\text{CO}_3\)) lowers the melting point of soda-lime glass to around \(1000\ ^\circ\text{C}\).
Summary
Key facts to remember.
- All glass types share basic properties: transparent, waterproof, hard but brittle, chemically inert, heat insulators, and electrical insulators.
- Fused silica glass: Pure \(\text{SiO}_2\), high melting point (\(1800\ ^\circ\text{C}\)), minimal expansion/contraction, used for telescope lenses.
- Soda-lime glass: \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{CaCO}_3\), low melting point (\(1000\ ^\circ\text{C}\)), easily moulded, prone to thermal cracking, used for bottles and jugs.
- Borosilicate glass: \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{CaCO}_3\), \(\text{B}_2\text{O}_3\), \(\text{Al}_2\text{O}_3\), heat-resistant with low expansion coefficient, used for laboratory glassware.
- Lead crystal glass: \(\text{SiO}_2\), \(\text{Na}_2\text{CO}_3\), \(\text{PbO}\), soft, dense, heavy with a high refractive index, used for prisms.
Short Activity
Complete all parts before checking your score.
A. Objective Quiz
Which of the following substances replaces calcium in glass to give it a higher density and a high refractive index suitable for prisms?
Why is borosilicate glass commonly used to manufacture laboratory beakers and flasks?
B. Fill in the Blanks
In the manufacturing of soda-lime glass, adding soda (\(\text{Na}_2\text{CO}_3\)) lowers the melting point of silica to around ______ °C.
Fused silica glass is made from silicon dioxide without adding any other chemical and is suitable to be used in making ______ lens.
C. Match the Type of Glass with Its Characteristic
Drag each glass type on desktop. On mobile, tap a glass type and then tap the matching box.
Type of Glass
Fused silica glass Soda-lime glass Borosilicate glass Lead crystal glassCharacteristic / Composition
Keywords
Tap or hover over a term to read its meaning.
