How to Read a Meniscus in Chemistry

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Liquids are difficult to measure with the naked eye due to surface tensions causing a meniscus to form on the circumference of the measuring object. In this article, you will learn what a meniscus is, why it forms and how you can accurately and precisely measure the volume of a liquid in laboratory graduated measuring glassware or plasticware.

What is Meniscus?

The meniscus of a liquid is the upward or downward curve seen at the top of a liquid in a container. The nature of curve whether upward (convex) or downward (concave) depends on the surface tension the liquid and its adhesion capacity to the wall of the container.

Concave Meniscus (See diagram A)

A concave meniscus occurs when the molecules of liquid are strongly attracted to the container wall rather than to each other. In that case, liquid appears to ‘stick’ from the edges forming a concave shape.

Convex Meniscus (See diagram B)

A convex meniscus appears when molecules of liquid are strongly attracted to each other rather than to the wall of container. Most liquids, including water, show a concave meniscus but a great example of a convex meniscus is liquid mercury in a glass container. It is to be noted that in some cases, the meniscus appears in a straight line instead of any curvature at all. For example, water in some plastic cylinders. No meniscus makes measuring very easy.

meniscus

How to read a meniscus correctly

You must get at eye-level with the meniscus to obtain an accurate reading. Pick up the glassware to bring it up to eye level or bend down to take a measurement.

The key to getting an accurate reading, is to measure the center of the meniscus whether it be concave or convex. E.g. with a concave meniscus, measure the bottom of the meniscus and for convex meniscus, take the reading from the top of the meniscus. (See diagram reading line in the diagram A and B).


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