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Liquid Volume

In science labs around the world, scientists need to make liquid measurements. To make up any solution of a known concentration, for example, the exact amount of liquid added (often water, H2O) is required. Medicines like cough syrup, antacids, and other medications must be of precise concentrations. This means that there must be a known amount of the medicine dissolved in a known amount of water. Knowing how to accurately measure the volume of liquids is therefore very important.

The standard unit of liquid volume in the metric system is the liter (L). For smaller quantiles, liters are too large so we use another unit of metric measurement, the milliliter (ml). From what you already know about metric prefixes, you might have already figured out that a milliliter is one one-thousandth (1/1,000) of a liter. Another way of saying this is that each liter of a liquid contains 1,000 milliliters.

Measuring Volume with Volumetric Containers

LabLearner comes with a number of different pieces of scientific equipment to accurately measure the volume of samples. These include: graduated cylinders, beakers, Erlenmeyer flasks, a one liter (1 L) pitcher and both 15 ml and 50 ml graduated centrifuge tubes.

With all of these different volumetric containers, your first question may well be, “which container do I use for measuring volumes?”. In general, while beakers and Erlenmeyer flasks have graduation markers on them, we don’t use them for accurately measuring volume. These pieces of equipment are used for mixing or heating solutions. The volume markings only give approximate readings and there is quite a large volume difference between the markings.

As a rule, the finer or the more graduation marks on a piece of volumetric equipment, the greater its accuracy. Notice, for example, that the individual marks on your 1000 ml graduated cylinder represent steps of 10 ml (right). Therefore, any volume between these 10 ml marks can only be estimated. On the other hand, if you examine your 100 ml graduated cylinder (right), you will see that the individual marks on it represent only 1 ml. Therefore, you can get better accuracy with the 100 ml graduated cylinder than the 1,000 ml (1 liter or 1 L) graduated cylinder.

Your LabLearner lab also contains 15 ml and 50 ml centrifuge tubes that you can use for measuring volume (below). These tubes are not primarily used for measuring volumes, but they are very easy to use and the 15 ml centrifuge tube, in particular, can measure small volumes with good accuracy. As in the case of the graduated cylinders, the smaller of the two centrifuge tubes offers the greater accuracy as its markings go down to a half of a milliliter (0.5 ml). Actually, if you look very closely, you will see that the pointed tip of the 15 ml centrifuge tube has graduations of 0.1 ml. However, for volumes of less than 1 ml, scientists would use more sophisticated instruments.

Finally, LabLearner comes with plastic pipettes that can be used to add and subtract liquid from any graduated container by the drop. Practice using these pipettes for greater accuracy.

LabLearner Tabs: Volumetric Containers

Learn more about volumetric containers by clicking on the tabs below. Start with Tab One: Using Volumetric Containers. Then move on to the next tab Tab Two: Example Graduated Cylinder Readings in order to see examples of measurements made with this very important piece of scientific equipment.

 

 

Using Volumetric Containers

1. Volumetric equipment includes the beakers, graduated cylinders, Erlenmeyer flasks, liter pitcher, and graduated centrifuge tubes. This equipment is used to measure the volume of  liquids in milliliters (ml).

2. Before measuring a liquid, place the piece of volumetric equipment on a flat level surface, such as a table.

3. Turn the piece of equipment so that the volume graduations can be seen easily.

4. Move (you may need to squat down, for example) so that you can view the graduations at eye level. This will allow you to take an accurate reading of a liquid’s volume.

5. If using a centrifuge tube, hold it in your hand at eye level and turn the graduations toward you.

6. Pour the liquid slowly into the piece of equipment so that you do not pass the volume that is being measured.

7. If measuring 50 ml, for example, add liquid until the surface of the liquid is even with the 50 ml mark on the piece of equipment.

8. If you should pour more liquid into the piece of equipment than is needed, remove the excess liquid with a plastic pipette or slowly pour some of the liquid out.

Example Graduated Cylinder Readings

You may notice that the surface of a liquid in a graduated cylinder or centrifuge tube may be slightly curved. This curved surface is called a meniscus. The meniscus is caused by an attraction between the surface of the liquid and the material that the cylinder is made of. When “reading” at a meniscus, always read at the bottom of it as in the picture below:

Below are five readings of a 100 ml graduated cylinder. For practice, try to pour each of these volumes of water into your own 100 ml graduated cylinder. The meniscus might not be as pronounced as in this drawing.