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How to Measure Liquid Volume

How to Measure Liquid Volume
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  • 0:02 Measuring Liquids
  • 1:20 Graduated Cylinders
  • 3:28 Burets
  • 5:48 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

There are many tools for measuring liquid volume. The tool you use will depend on how much liquid you have to measure and how precise you need to be. Learn how graduated cylinders and burets are used to get accurate liquid volume measurements.

Measuring Liquids

When I'm in the kitchen mixing up the ingredients for my grandmother's delicious chocolate cake, I add vegetable oil to the mixing bowl using a measuring cup. Measuring cups are great kitchen tools for measuring liquid ingredients, like oil. However, measuring cups don't hold water when it comes to working in a laboratory.

Scientific experiments often use liquids that need to be measured to exact amounts. For some experiments, being off by a few milliliters could alter the result. Because measurements need to be exact, a scientist needs the right tool for measuring liquid volume. The tool the scientist selects will depend on how much liquid he must measure and how precise he needs to be.

If he simply needs a ballpark figure, he might use a beaker or flask, which would be like using measuring cups in your kitchen. Beakers and flasks might have volume markings on them, but due to their shape, it's hard to get a precise measurement using these tools.

In this lesson, we will focus on two tools you can use to accurately measure liquid volume, namely graduated cylinders and burets.

Graduated Cylinders

Graduated cylinders are aptly named because they are cylindrical containers with markings on the side, known as graduations. These graduations vary with the size of the graduated cylinder.

If the cylinder is big, and can hold 500 mL of liquid, then the markings on the graduated scale would be divided into 5 mL increments. Five mL is about a teaspoon of liquid. If the cylinder is small and holds only 10 mL of liquid, then the markings would be in 0.1 mL increments, which is a tiny droplet.

Graduated cylinders are typically made of glass or plastic, which is actually significant. It's important because we know that water and other liquids tend to cling to these materials. This attraction of liquid to the container causes the water level to be slightly higher at the edges and lower in the middle. This creates a meniscus, which is the term we use to describe the curved surface that results when a liquid is inside a container.

When you read the level of water inside the graduated cylinder, you want to measure the level at the bottom, which is the middle, of the meniscus. If you took your reading where the liquid meets the container, your reading would be too high. Speaking of ways to get an accurate reading, it's important that you take your reading at eye level, so your measurement is not distorted by your view.

As an example, let's say you have a glass of water, and you want to know the amount you have down to the milliliter. You can grab a 100 mL graduated cylinder and pour the water into the opening at the top of the cylinder. You can then crouch down so your eyes are at the same level of the water surface. This allows you to see the meniscus, or curve of the water level. You can now eyeball the lowest point of the meniscus and take your reading using the markings on the outside of the cylinder.

Burets

You just learned a good way to measure liquid volume, but some experiments require you to be even more precise. In these cases, you might want to use burets. Burets are cylindrical containers with graduations marked on the side and a valve at the bottom. The valve at the bottom of the buret, which is called the stopcock, allows you to flow or drip precise amounts of liquid into a receiving container.

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