How to Read a Meniscus in Chemistry

How to Read a Meniscus in Chemistry

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The meniscus is the curve seen at the top of a liquid in response to its container. The meniscus can be either concave or convex, depending on the surface tension of the liquid and its adhesion to the wall of the container.

A concave meniscus occurs when the molecules of the liquid are more strongly attracted to the container than to each other. The liquid appears to "stick" to the edge of the container. Most liquids, including water, present a concave meniscus.

A convex meniscus (sometimes called a "backwards" meniscus) is produced when the molecules of the liquid are more strongly attracted to each other than to the container. A good example of this shape of meniscus can be seen with mercury in a glass container.

In some cases, the meniscus appears flat (e.g., water in some plastics). This makes taking measurements easy.

How to Take Measurements With a Meniscus

When you read a scale on the side of a container with a meniscus, such as a graduated cylinder or volumetric flask, it's important that the measurement accounts for the meniscus. Measure so that the line you are reading is even with the center of the meniscus.

For water and most liquids, this is the bottom of the meniscus. For mercury, take the measurement from the top of the meniscus. In either case, you are measuring based on the center of the meniscus. For a flat meniscus, make sure the liquid is level. Usually placing the container on a lab bench does the trick.

You won't be able to take an accurate reading looking up at the liquid level or down into it. Get eye level with the meniscus. You can either pick up the glassware to bring it to your level or else bend down to take measurements in situations where you're 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.

Fun Fact: The word meniscus comes from the Greek word for "crescent." This makes good sense, considering the shape of a meniscus. In case you're wondering, the plural of meniscus is menisci.

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