Problem 131 - A Complete Resource Book in Chemistry for JEE Main

Question

For making good quality mirrors, plates of float glass are used. These are obtained by floating molten glass over a liquid metal, which does not solidify before glass. The metal used can be [2003] (a) mercury (b) tin (c) sodium (d) magnesium

Step-by-Step Solution

Answer

Tin is used because it has a suitable melting point for the float glass process.

Step 1: Understand the Properties of Liquid Metals

To determine which metal is used in the float glass process, first consider that the metal should be in liquid form at a temperature where the glass can also remain in a moldable state. This requires a relatively low melting point metal which does not solidify before the glass does.

Step 2: Analyze the Candidate Metals

Now, analyze the melting points of the given options: - Mercury: Melts at -39°C - Tin: Melts at about 232°C - Sodium: Melts at 98°C - Magnesium: Melts at 650°C Mercury remains liquid at all practical temperatures for glass processing, but its high toxicity excludes it from this application.

Step 3: Conclusion Based on Melting Points

The most suitable choice of metal for this process is Tin, as it melts at 232°C, matching the requirements of the float glass production process where the glass solidifies after the metal. Tin provides a stable and non-toxic solution.

Key Concepts

Melting Points of Metals

Understanding the melting points of metals is crucial when considering materials for specific industrial processes, like glass production.
Metals transition from solid to liquid at specific temperatures, known as melting points.

Common metals and their melting points:

• Mercury: -39°C
• Tin: 232°C
• Sodium: 98°C
• Magnesium: 650°C

In the context of the float glass process, the chosen metal must remain liquid at temperatures where glass can still be shaped, which makes tin an ideal candidate.
Understanding such properties is essential when selecting materials for heat-dependent manufacturing processes.
Tin's melting point is particularly compatible with glass production needs, allowing it to stay liquid while providing a smooth surface for glass to spread and solidify.

Properties of Liquid Metals

Liquid metals have unique characteristics that differ from their solid states.
They play an important role in processes like the float glass production, where maintaining a liquid state under specific conditions is key.

Some amazing properties of liquid metals include:

• High thermal conductivity, allowing them to evenly distribute heat.
• Fluidity, which makes them perfect for creating smooth surfaces underneath molten glass.
• Surface tension, helping to avoid oxygen bubbles in the glass.

In the float glass process, tin is used due to its liquid properties at certain temperatures, assisting in the production of defect-free glass with minimal waste.
Understanding these attributes helps explain why tin is preferred over other candidate metals like mercury or sodium in this application.

Glass Production

Glass production is a fascinating process that involves shaping and solidifying silica-based materials.
The float glass process is a commonly used method, named for the technique of floating molten glass over a pool of liquid metal, usually tin.

Stages of Float Glass Production:

• Melting: Raw materials such as sand, soda ash, and limestone are melted at high temperatures.
• Molding: Molten glass is poured onto a pool of liquid tin, ensuring a flat and even surface.
• Cooling: The glass slowly cools and solidifies as it moves across the metal surface, forming the final product.

This method produces uniform, high-quality glass sheets that are essential for items like windows and mirrors.
The understanding of these stages is vital for anyone studying material science or manufacturing technologies.

Chemical Properties of Tin

Tin is a critical element in various industrial applications due to its chemical and physical properties.
It belongs to the "poor metals" group and exhibits significant stability at moderate temperatures.

Key chemical properties of tin include:

• Non-toxicity, making it safer for certain applications compared to metals like lead or cadmium.
• Resistance to corrosion, which is vital in maintaining the integrity of materials over time.
• Ability to form alloys, enhancing its usefulness in soldering and other metallurgical processes.

In the float glass process, tin's low reactivity ensures that it doesn’t interfere with the glass components, maintaining clarity and quality.
Being aware of these properties aids in the understanding of tin's widespread usage and its role in various manufacturing processes.