watch glass
Definition
A watch glass is a circular, slightly concave piece of glass that is used in science laboratories. It is typically made of borosilicate glass, which is a type of glass that is resistant to heat and chemicals.
Watch glasses are used to hold small amounts of liquids or solids, such as chemicals, samples, or precipitates. They can also be used to cover beakers or flasks to prevent evaporation.
Watch glasses are a versatile tool that can be used in a variety of scientific experiments. They are an essential piece of equipment for any science lab.
Here are some other uses of watch glasses:
- To evaporate a liquid to concentrate it.
- To heat a small amount of a substance.
- To weigh a small amount of a substance.
- To hold a small amount of a substance for observation.
- To cover a Petri dish to prevent contamination.
How can the word be used?
The scientist placed a watch glass over the microscope slide.
Different forms of the word
Noun: watch glass (plural: watch glasses).
Adjective: watch-glass.
Verb: to watch-glass.
Etymology
The word "watch glass" comes from the Old English word "wæcce", meaning "to watch", and "glæs", meaning "glass".
The first recorded use of the word "watch glass" was in the 17th century.
Question
When might a watch glass be used?
AQA Science Exam Question and Answer
Question:
Explain the purpose and use of a watch glass in laboratory settings. Discuss how a watch glass is employed in various scientific tasks and experiments.
Answer:
A watch glass is a concave, circular piece of glass commonly used in laboratory settings for various purposes. It serves as a versatile tool in scientific experiments and tasks, owing to its unique design and properties.
One primary function of a watch glass is to cover and protect small samples or substances during experimentation. Placing a watch glass on top of a beaker or container helps prevent contamination, evaporation, or unwanted interactions with the external environment. It also allows observation of reactions while providing a barrier.
Moreover, a watch glass can be used for evaporating liquids. When a small amount of liquid is placed on the concave surface, the larger surface area facilitates faster evaporation, making it useful for tasks like crystallisation or concentrating solutions.
A watch glass can also serve as a platform for small-scale reactions, such as mixing and precipitation. Its flat and smooth surface makes it suitable for grinding solids into powders or testing the solubility of substances.
In chemistry, it finds application in procedures like sublimation, where solids are transformed directly into vapour without melting, and in covering crucibles during heating to prevent splattering.