Measurement: Volume and Temperature

Measuring Volume and Temperature

Another measurement that you will be doing frequently is to measure the volume of a substance. We often think only of measuring volumes of liquids, but all matter takes up space so all matter has a volume (even gasses!). We'll discuss how to take accurate volume measurements and then you'll get a chance to try it out in the lab. This section will also review measuring temperatures accurately and precisely.

Volumes of Liquids

In this class, you'll most often measure the volume of a liquid using a graduated cylinder. There are other types of glassware that can measure volume but, for our purposes, graduated cylinders have enough precision as well as being relatively easy to use.

You should be able to measure the volume of liquids in a graduated cylinder. How precisely you can measure volume depends on the size and type of graduated cylinder you use. Generally, you should be able to estimate between the etched or printed lines.

It is important to notice what each line or interval on the graduated cylinder represents. Different kinds of graduated cylinders are set up differently. A 10 milliliter cylinder, for example, usually has one tenth of a milliliter for each graduation, but some have two-tenths milliliter for each graduation. The way to check this is to count the divisions between consecutive numbers. Here we have the usual 10 divisions from one number to the next; therefore, the volume increment for each of those lines is a tenth of a milliliter. Estimating your measurements by reading between the lines, you should be able to measure to a hundredth of a milliliter.

On this 100 milliliter cylinder, the numbers are 10, 20, 30, etc., so there is a 10 milliliter increment between them. Since there are 10 divisions between consecutive numbers, each division represents one milliliter. Therefore, you should be able to estimate to tenths of a milliliter by reading between the lines.

On some cylinders, there may only be five divisions between numbers. Or there may be ten divisions for a 2 milliliter increment. In these cases, each of the divisions represents 0.2 milliliters, rather than 0.1. You need to be aware of that when you're using the cylinders like these, and adjust your between-line-estimates accordingly.

The Meniscus

A characteristic of liquids in glass containers is that they curve at the edges. This curvature is called the meniscus. You measure the level at the horizontal center or inside part of the meniscus. With water in glass, the meniscus will curve up at the edges and down in the center so we say you read the bottom of the meniscus. The volume of liquid in this cylinder is 5.90 mL (not 6.10 mL!).

One other important technique when measuring volume is to view the meniscus at eye level; if you read the volume looking down (or up) at an angle, you will not get an accurate reading. Don't lift the graduated cylinder up off the counter but instead sit, bend, or squat down so that the cylinder stays on the counter and you bring your eye level down to the read the level of the meniscus.

Volumes of Solids

Solid samples also have volume. If they are powder or granular you can measure their volume the same as a liquid, a cup of flour or sugar, for example.

If the sample is in a regular geometric shape, its dimensions can be measured and its volume calculated.

The volume of a solid sample can also be measured by displacement. (Just be sure your solid won't dissolve in the water!) This usually involves three steps:

Measure the volume of liquid in a partially filled graduated cylinder,

Add solid (make sure it is submerged) and note the rise in the liquid level

Measure the combined volume of the solid and liquid.

The difference between the initial and final volumes is the volume of the solid

Temperature Measurements

Another objective for this lesson is to use the Celsius or centigrade temperature scale to measure the temperature of fluids. Liquids and gases are both fluids.

The laboratory thermometers we have are calibrated in degrees Celsius rather than degrees Fahrenheit.

The Celsius scale used to be called the centigrade. It was called centigrade because the difference between the freezing temperature of water and the boiling temperature of water is divided into 100 degrees. 0^oC is defined as the temperature at which water freezes and melts. 100^oC is defined as the temperature at which water boils (using normal pressure). It is the scale commonly used in scientific work and in everyday use in most countries.

The laboratory thermometers we use are partial immersion thermometers. This means they are calibrated to read correctly when the end of the thermometer (up to a certain mark) is in the liquid being measured but the temperature scale is not. When you are measuring temperatures, you might want to experiment to see how much difference it makes to vary the depth of the thermometer in the liquid.

These thermometers do not have to be shaken down. Quite a few laboratory thermometers have been broken by trying to shake them down next to a table.

It is best to hold a thermometer while using it. The container it is in may or may not be able to support it. All you have to do is put the thermometer in the liquid and watch the mercury or alcohol level change. When it stops changing, read the mercury level or the alcohol level if you use one of the red ones. That is your measurement. You don't have to wait a prescribed length of time, just let it come to a rest.

You may have turn the thermometer to see the numbers and line up the mercury or alcohol with the scale.

When you read them you should estimate between the lines, the same as you did with the length and volume measurements. Try to mentally divide the sections into 10 equal parts in order to read to a tenth of a degree.

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