Have you ever seen dry ice? When the ice chunks are exposed to the air, they quickly sublime (turn from solid to gas) which produces a thick misty fog like a witch's cauldron.

Dry ice is frozen carbon dioxide, and to touch it you need to be wearing special gloves. Why? Because dry ice is about -109 °F! If you were to touch that with your bare hands, you would get severe burns akin to frostbite, and nobody wants that!

The way dry ice is made is by injecting gaseous carbon dioxide into a tank, which is at a temperature of -109 °F. So how do they know the temperature of the tank in the first place? They can't exactly use a typical mercury thermometer since it would freeze too!

In this article, we will be learning how to measure temperature in the lab. We will be learning what temperature is, the tools used to measure it, and how to best measure it.

• The article focuses on measuring temperature in the lab.
• First, we bring up some questions you may have about measuring temperature.
• Next, we will define what temperature is and what it measures.
• Then, we will learn what units to use when measuring temperature.
• After that, we will look at some common tools used to measure temperature.
• Lastly, we will discuss the steps for measuring temperature.

Measuring temperature questions

If it's your first time in the lab, you probably have a bunch of questions:

• What do I use to measure temperature?
• What units should I measure in?
• How do I best measure temperature?
• What does temperature even measure?

Well, today we are going to be answering all your temperature-related questions. Keep reading to find out more!

Measuring temperature definition

When you think about temperature, you probably think about it in terms of how hot or cold something is. But what does temperature measure, really?

In other words, temperature is a measure of how fast particles move. At low temperatures, particles have very little movement, and will only vibrate in place. At high temperatures, particles are bouncing all around.

Different physical processes (like freezing/melting) and chemical processes (like chemical reactions) can only occur at certain temperatures/temperature ranges. Therefore, being able to accurately measure temperature is an important skill in the lab!

Measuring units of temperature

Here in the U.S., we measure temperature in Fahrenheit (°F). However, pretty much the entire rest of the world uses Celsius (°C). Because of this, it is common to measure temperature in Celsius, not Fahrenheit (even though it can be confusing at first).

For those of you who are just starting to use Celsius, here are some key points on the scale:

• 0 °C is the freezing point of water (32 °F).
• 100 °C is the boiling point of water (212 °F).
• 78.37 °C is the boiling point of ethanol (a common solvent) (173.1 °F).

If the apparatus you are using is in Fahrenheit, here is the equation to convert between units:

$$(x^\circ F-32)*\frac{5}{9}$$

For example, say you get a reading of 70.2 °F:

$$(x^\circ F-32)*\frac{5}{9}$$

$$(70.2^\circ F-32)*\frac{5}{9}=21.2^\circ C$$

Technically speaking, the standard unit of temperature for scientists is Kelvin (K). However, you will commonly see scientists using Celsius, and many temperature reading tools are also in Celsius.

The conversion between these units is:

$$x^\circ C+273.15=K$$

Measuring tools of temperature

When you think of temperature tools, what images pop up into your mind? The mercury-filled thermometer on your fridge? Or maybe the thermometer you put in your mouth when you are sick? While these are both valid ways of measuring temperature, they aren't common in the lab.

The most common thermometers used in the lab are called probe thermometers.

Fig.1-A probe thermometer

The long metal stick (shown above) is the titular "probe". The probe is placed inside the solution whose temperature you are measuring. The screen portion will then display the temperature.

While they are less common, mercury thermometers can be used in the lab.

Fig.2-A mercury thermometer

The red liquid inside the thermometer is mercury. When mercury is heated, it expands, causing it to move up the thermometer and display the temperature. When it is cooled, it contracts, causing it to move downward.

These thermometers are less common since you have to manually read the temperature, which can lead to errors if read incorrectly.

Ways of measuring temperature

Now that we know our tools of the trade, let's talk about the best practices for actually measuring temperature. Below are the steps to properly measure temperature:

1. (If digital) Turn on the thermometer, making sure it is measuring in the correct units and is calibrated
   • If the device cannot measure in the desired units, make sure to convert before using the measurement(s) in any calculations.
   • The best way to calibrate thermometers is by placing them in ice water for at least 30 seconds. The freezing point of water is 0 °C, so you adjust the thermometer until it reads that temperature.
2. Place the thermometer inside the solution
   • Make sure the thermometer is not touching the glass of the beaker/walls of the container. This will instead give you the temperature of the glass.
3. Swirl the thermometer around the solution
   • Swirling ensures that the temperature throughout the solution is uniform
4. Wait for the thermometer to reach the temperature of the species
   • Do not write down the temperature until the temperature reading has not changed for at least 3 seconds
5. Repeat steps 2-4 a few times to ensure the accuracy of the measurement
   • Typically, you would use the average of your measurements as the "correct" temperature reading

When measuring temperature, or any variable really, we want to be as accurate as possible. Because of this, it is best to follow the steps above. Having the correct temperature value is important for not only calculations but also, so you can better understand what is happening in your experiment.