This article has been written in order to help chemistry students understand how to correctly read a meniscus.
What is Meniscus?
A meniscus is a curve that is seen at the top of a liquid in response to its container. The meniscus can be em concave or convex, depending on the surface tension of the liquid and adhesion to the wall of the container.
The meniscus is a Greek word meaning Crescent. The plural of the word Menuscus is Menisci.
- We say a Meniscus is Concave when the molecules of the liquid are more strongly attracted to the container than to each other. The liquid will appear to “stick” to the edge of the container. It is important to note that most liquids, including water, present a concave meniscus.
- A Meniscus is Convex when the molecules of the liquid are more strongly attracted to each other than to the container. An example of a Convex meniscus can be seen in mercury in a glass container. In some cases, the meniscus appears flat (for example, water in some plastics). This makes taking measurements easy.
When you read a scale on the side of a container with a Meniscus, such as a graduated cylinder or volumetric flask, it is important that the measurement accounts for the meniscus.
- The line you are reading should be even with the centre of the meniscus. In water and most liquids, this can be found in the bottom of the meniscus. For mercury, the measurement should be taken from the top of the meniscus. In either case, you are to measure based on the centre of the meniscus.
- In order to get an accurate reading, get eye-level with the meniscus and not below or above it. You can either pick up the glassware to bring it up to your level or bend down to take measurements in situations where you are concerned with dropping the container or spilling its contents. Use the same method to take measurements each time so that any errors you make will be consistent.