Watch Glass Uses, Functions and Importance

Watch glass is simple in structure, yet it proves to be extremely important for scientists in many ways. It is a glass watch with an almost circular and concave design, frequently made out of glass or other see-through materials. Being a watch glass, it is used predominantly for sample preparation, evaporation, covering, and weighing purposes. This article elaborates on what is a watch glass, its uses and advantages, types of watch glasses, and safety measures for such types of glass.

What is a Watch Glass?

A watch glass resembles the lid of a pocket watch, having a circular dome shape. It is primarily used in laboratories and schools for various purposes, such as increasing the rate at which a liquid evaporates, serving as a lid for beakers, or balancing items. A watch glass function is manufactured from soda-lime glass or borosilicate glass, both of which are strong types of glass. The concave shape enables liquids and solids to be stored without the risk of spilling, thus increasing its range of applications.

In every laboratory, there are different sizes of watch glasses available, ranging from 50mm to 150mm. With the shortcut aim of looking at a sample under observation, most watch glasses tend to be clear. They may be predominantly used in chemistry labs, but they are also found in biological, environmental, and other educational institutes.

Key Features of a Watch Glass

Material Composition

• Borosilicate glass is the most common material found in watch glasses because it is designed to withstand chemical and heat damage.
• Additionally, some watch glasses are made out of quartz for specific experimental environments with increased heat.
• The clarity of the glass watch allows one to view the contents without removing the lid.

Concave Shape

• These slight angles serve two functions: holding liquids without spilling and increasing the surface area for evaporation.
• Moreover, it prevents particles or contaminants from entering or exiting the container when used as a cover.

Variety of Sizes

• Watch glasses are available in different sizes, which makes them versatile for various laboratory applications.

Watch Glass Uses in Laboratory

In the laboratory, possibly the simplest of materials is the watch glass, but in practice, it serves many purposes. Here are some of the most common watch glass uses in a laboratory:

• Evaporation of Solvents: The watch glass is usually used for evaporating solvents or small amounts of liquid. The concave shape makes it easy to hold liquid, making evaporation efficient.
• Covering Beakers and Flasks: A watch glass chemistry may be used to cover a beaker when performing acid-base titrations, preventing spills while boiling solutions.
• Small Reactions: If microscale reactions are to be performed, a watch glass is an excellent reaction medium. Its transparency allows easy observation of color changes and new substance formations.
• Sample Preservation: Watchglasses are commonly used to filter, dry, or store small samples in various scientific processes, including gravimetric analysis.
• Qualitative and Quantitative Analysis: Watch glasses are used in solution evaporation to encourage crystallization while preventing contamination.

Types of Watch Glasses

Different types of watch glasses serve distinct purposes in a laboratory:

Standard Borosilicate

• Commonly used for weighing, evaporating, and covering beakers.
• Strong, shock-resistant, and heat-resistant.

High-Temperature Quartz

• Suitable for high-temperature experiments.
• Can withstand extreme heat better than borosilicate glass.

Frosted 

• Features a matte finish to reduce glare or reflection.
• Useful in situations where light reflection interferes with observations.

Colored

• Used in light-sensitive experiments.
• Protects samples from damaging light exposure.

Benefits of Using Watchglasses in Laboratories

• Heat Resistance: Borosilicate watch glasses are low-expansion and ideal for heat-sensitive experiments.
• Chemical Resistance: Can withstand highly reactive chemicals without degradation.
• Ease of Use: Lightweight, simple to clean, and easy to handle.
• Economical: Cost-effective due to durability.
• Non-reactive Surface: Inert glass does not react with samples.

Precautions When Handling Watch Glasses

• Handle with Care: Avoid dropping watchglasses as they can shatter.
• Avoid Sudden Temperature Changes: Rapid heating or cooling can cause breakage.
• Use Proper Tools: Utilize tongs or heatproof gloves when handling heated.
• Avoid Overheating: Even heat-resistant watch glasses can be damaged by thermal shock.
• Proper Storage: Store in safe locations to prevent impact damage.

Conclusion

Despite its straightforward design, a watch glass in chemistry is one of the most essential laboratory tools. Its multifunctional nature allows it to serve various purposes, from evaporation to weighing samples, and even covering beakers. Made from borosilicate or quartz, watch glasses can tolerate high temperatures and resist chemical reactions, making them suitable for scientific research and experiments. Understanding the types, benefits, and safety measures of watch glasses ensures their effective and safe usage in laboratories.

FAQs

What is a watch glass used for in chemistry?

A watch glass is primarily used in chemistry laboratories for evaporation, covering beakers, conducting microscale reactions, and holding samples for weighing or drying.

Why is a watch glass concave in shape?

The concave shape of a watch glass helps prevent spilling, increases the surface area for evaporation, and allows safe containment of liquids or solids.

Can a watch glass be heated directly?

Although watch glasses are heat-resistant, direct exposure to flames or rapid temperature changes can cause thermal shock and breakage. It is recommended to gradually increase heat instead.